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THE

SUBTERRANEAN WORLD.

LONDON: PRINTED BY

SPOTTISWOODE AND CO., NEW-STREET SQUARE

AND PARLIAMENT STREET

CARBONIFEROUS FOREST, CARBONIFEROUS PERIOD.

THE
SUBTERRANEAN WORLD.

BY

DR. GEORGE HARTWIG,

AUTHOR OF

‘THE SEA AND ITS LIVING WONDERS,’ ‘THE TROPICAL WORLD,’ ‘THE POLAR WORLD,’

AND ‘THE HARMONIES OF NATURE.’

WITH THREE MAPS AND NUMEROUS ENGRAVINGS ON WOOD.

NEW YORK:

SCRIBNER, WELFORD, AND CO.

1871.

PREFACE.

Nature displays her wonders not only in the starry heavens or in the boundless variety of animal and vegetable life on the surface of our earth. In the dark regions underground she likewise shows us much that is remarkable or beautiful, or carries on gigantic operations, which are sometimes beneficent and sometimes disastrous to mankind.

There lie concealed the mysterious laboratories of fire, which reveal to us their existence in earthquakes and volcanic explosions. There, in successive strata, repose the remains of extinct animals and plants. There many a wonderful cavern may be seen, with its fantastic stalactites, its rushing waters, and its noble halls. There have been deposited the rich stores of mineral wealth—the metals, the coals, the salt, the sulphur, &c.—without whose aid man would never have been more than a savage.

The aim of the present work has been to describe the wonders of this hidden world in their various relations to man, now raising him to wealth, and now dooming him to destruction.

The author trusts that he may have succeeded in giving a sketch of the phenomena resulting from the action of subterranean forces, which, with his account of the wonders of the sea, of the tropics, and of the frozen regions, may impart to the reader a fair idea of the history and present condition of the wonderful world in which we live.

Salon, near Ludwigsburg:

July 6, 1871.

CONTENTS.

LIST OF ILLUSTRATIONS.

WOODCUTS.

The following is a list of the full-page illustrations, included in the foregoing list, all of which, except No. 2, are engraved by G. Pearson:—

CHAPTER I.
GEOLOGICAL REVOLUTIONS.

The Eternal Strife between Water and Fire—Strata of Aqueous Origin—Tabular View of their Chronological Succession—Enormous Time required for their Formation—Igneous Action—Metamorphic Rocks—Upheaval and Depression—Fossils—Uninterrupted Succession of Organic Life.

Geology teaches us that, from times of the remoteness of which the human mind can form no conception, the surface of the earth has been the scene of perpetual change, resulting from the action and counter-action of two mighty agents—water and subterranean heat.

Ever since the first separation between the dry land and the sea took place, the breakers of a turbulent ocean, the tides and currents, the torrents and rivers, the expansive power of ice, which is able to split the hardest rock, and the grinding force of the glacier, have been constantly wearing away the coasts and the mountains, and transporting the spoils of continents and islands from a higher to a lower level.

During our short historical period of three or four thousand years, the waters, in spite of their restless activity and the considerable local changes effected by their means, have indeed produced no marked alteration in the great outlines of the sea and land; but when we consider that their influence has extended over countless ages, we can no longer wonder at the enormous thickness of the stratified rocks of aqueous origin which, superposed one above the other in successive layers, constitute by far the greater part of the earth-rind.

Our knowledge of these sedimentary formations is indeed as yet but incomplete, for large portions of the surface of the globe have never yet been scientifically explored; but a careful examination and comparison of the various strata composing the rocky foundations of numerous countries, have already enabled the geologist to classify them into the following chronological systems or groups, arranged in an ascending series, or beginning with the oldest.

Each of these systems consists again of numerous sections and alternate layers, sometimes of marine, sometimes of freshwater formation, the mere naming of which would fill several pages.

When we reflect that the Laurentian system alone has a thickness of 30,000 feet; that many of the numerous subdivisions of the Triassic or Oolitic group are 600, 800, or even several thousand feet thick, and that each of these enormous sedimentary formations owes its existence to the disintegration of pre-existing mountain masses—we can form at least a faint notion of the enormous time which the whole system required for its completion.

TABULAR GEOLOGICAL PROFILE.

TABULAR GEOLOGICAL PROFILE.

STRATA
		1. Recent Deposits
T E R T I A R Y		2. Pliocene
		3. Miocene.
		4. Eocene
S E C O N D A R Y		5. Cretaceous
		6. Oolitic
		7. Lias
		8. Triassic
P R I M A R Y		9. Permian
		10. Carboniferous
		11. Devonian
		12. Silurian
		13. Cambrian
		14. Laurentian

CHARACTERISTICS FOSSIL REMAINS
	1. Recent Deposits. Irish Elk
	2. Pliocene. Mastodon.
	3. Miocene. (1) Cerithium. (2) Segnoia.
	4. Eocene. (1) Nummulites. (2) Natica.
	5. Cretaceous. (1) Inoceramus. (2) Turrilites. (3) Pecten. (4) Hamites.
	6. Oolite. (1) Pholadomya. (2) Trigonia. (3) Mantellia. (4) Nerinæa.
	7. Lias. (1) Icthyosaurus. (2) Ammonites.
	8. Triassic. (1) Labyrinthodon. (2) Encrinus.
	9. Permian. (1) Bakewellia. (2) Productus. (3) Palæoniscus.
	10. Carboniferous. (1) Goniatites. (2) Lepidodendron. (3) Calamites.
	11. Devonian. (1) Pterichthys.
	12. Silurian. (1) Goniatites. (2) Lepidodendron. (3) Calamites.
	13. Cambrian. (1 Strophomena. (2) Lingula. (3) Pentamerus. (4) Calymene.
	14. Laurentian. (1) Oldhamia.

Had the levelling power of water never met with an antagonistic force, there can be no doubt that the last remains of the dry land, supposing it could ever have risen above the ocean, must long since have been swept into the sea. But while water has been constantly tending to reduce the irregularities of the earth’s surface to one dull level, the expansive force of subterranean heat has been no less unceasingly active in

restoring the unevenness of the external crust by the ejection or protrusion of new masses of stone (porphyry, trachyte, basalt, lava, &c.), and by the consequent disturbance, in a variety of ways, of the stratified rocks.

AQUEOUS STRATA DISTURBED BY IGNEOUS FORMATIONS.
B C D, aqueous strata, originally horizontal, raised by protrusion of A, granitic rock.

Plutonic and volcanic eruptions and upheavings, in their reaction against the levelling tendencies of water, have in many places deranged, broken, fractured, contorted, or raised strata deposited in horizontal layers at the bottom of the sea, or of large inland lakes. Sometimes a huge mass of crystalline rock, glowing from the furnaces of the deep, has, by its irresistible expansion, slowly forced its way through the superincumbent sedimentary formations, which, yielding to the pressure from below, now form vast mountain slopes, or vertical rock walls, or have even been so totally inverted that strata of a more ancient formation now overlie those of more modern date, and excite the wonder of the puzzled geologist.

Sometimes, also, volcanic eruptions, repeated through a long lapse of ages and constantly accumulating lavas and cinders, have at length piled up large islands, such as Iceland or Madeira, which now raise their summits thousands of feet above the ocean.

But subterranean fire, and its assistant, steam, have not only produced vast mechanical changes; they have also been the frequent causes of great chymical metamorphoses in the rocks subjected to their action. To the calcining, decomposing, and vapour-generating effects of heat, we trace the origin of the marble of Carrara, of alabaster, of gypsum, and all those various species of stone which geologists include under the name of metamorphic rocks.

Besides the more paroxysmal and violent revolutions resulting from the action of subterranean fire, we find that the earth-rind has at all times been subject to slow oscillatory movements of upheaval and subsidence, frequently alternating on the same spot with long periods of rest. The greater part of the actual dry land has been deep sea, and then again land and ocean many times in succession; and doubtless the actual sea bottom would exhibit similar alternations were we able to explore it. The same materials have repeatedly been exposed to all these changes—now raised or poured out by subterranean[subterranean] fires, and then again swept away by the waters; now changed from solid rock into sand and mud, and then again converted, by pressure or heat, into solid rock. Thus the history of the earth-rind opens to us a vista into time no less grand and magnificent than the vista into space afforded by the contemplation of the starry heavens.

The oldest and the newest stratified rocks are composed of the same mineral substances; for clay, sandstone, and limestone occur in the Silurian and in the Carboniferous formation; in the Cretaceous and Triassic systems; in the Tertiary and in the Alluvial deposits, which have immediately preceded the present epoch.

Where then, it may be asked, does the geologist find a chronological guide to lead him through the vast series of strata which, in the course of countless ages, have been deposited in the water? How is he able to distinguish the boundaries of the various periods of creation? Where are the precise indications which enable him to decipher the enigmas which the endless feuds of fire and water have written in the annals of our globe?

The fossil remains of animals and plants wonderfully furnish the guidance which he needs. The corals and shells, the ferns and conifera, the teeth and bones found in the various strata of the earth-rind are the landmarks which point out to him his way through the labyrinth of the primitive ages of our globe, as the compass directs the mariner over the pathless sea. Every leading fossil has its fixed chronological character, and thus the age of the formation in which it occurs may be ascertained, and its place determined in the geological scale. It would, however, be erroneous to suppose that each successive formation has been the seat of a totally distinct creation, and that the organic remains found in one particular stratum are separated by an impassable barrier from those which characterise the preceding or following sedimentary deposits.

As on the surface of the earth or along the shores of the sea, each land or each coast has not only its peculiar plants or animals, but also harbours many of the organic forms of the neighbouring countries or conterminous shores; as the tropical organisations gradually pass into those of the temperate zones, and these again merge into those of the polar regions, so also the stream of life has from the first flowed uninterruptedly, in gradually changing forms, through every following age. New genera and species have arisen, and others have disappeared, some after a comparatively short duration, others after having outlasted several formations; but every extinct form has but made way for others, and thus each period has not only witnessed the decay of many previously flourishing genera and species, but has also marked a new creation.

No doubt the numerous local disturbances above mentioned have frequently broken the chain of created beings; but a gradual progress from related to related forms, a continuous development from lower to more highly organised species, genera, orders, and classes, has from the beginning been the general and constant law of organic life. Universal destructions of existing forms, revolutions covering the whole surface of the earth with ruin, have most assuredly never occurred in the annals of our globe.

Nor must it be supposed that the whole scale of sedimentary formations is to be found superimposed in one spot; for as in our times new strata are chiefly growing at the mouths of rivers, or where submarine currents deposit at the bottom of the ocean the fine mud or sand which is conveyed into the sea by the disintegration of distant mountain chains, so also from the beginning each stratum could only have been deposited in similar localities; and while it was slowly increasing, and not seldom acquiring colossal dimensions in some parts of the globe, others remained comparatively but little altered, until new oscillatory movements produced a change in their former position, and opening new paths to the rolling waters, here set bounds to the progress of one formation, and there favoured the deposition of another.

A complete study of all the various transformations by fire or water which the surface of our earth has undergone would require an elaborate treatise of geology, and lies far beyond the scope or the pretensions of a popular volume which is chiefly devoted to the description of caves and mines. But I should be neglecting some of the most interesting features of the subterranean world, were I to omit all mention of the fossils imbedded in its various strata; of its internal heat; of the upheavals and subsidences which have played so conspicuous a part in the history of the earth-rind, and are still proceeding at the present day; of the water percolating or flowing beneath the earth’s crust, and finally of the volcanoes and earthquakes, which prove to us that the ancient subterranean fires, far from being extinct, are still as powerful as ever in remodelling its surface.

CHAPTER II.
FOSSILS.

General Remarks—Eozoon Canadense—Trilobites—Brachiopods—Pterichthys Milleri—Oldest Reptiles—Wonderful Preservation of Colour in Petrified Shells—Primæval Corals and Sponges—Sea-lilies—Orthoceratites and Ammonites—Belemnites—Ichthyosaurus and Plesiosaurus—Pterodactyli—Iguanodon—Tertiary Quadrupeds—Dinotherium—Colossochelys Atlas—Megatherium—Mylodon—Glyptodon—Mammoth—Mastodon—Sivatherium Giganteum—Fossil Ripple-marks, Rain-drops, and Footprints—Harmony has reigned from the beginning.

The fossil remains of plants and animals, which have successively flourished, and passed away since the first dawn of organic life, occupy a prominent place among the wonders of the subterranean world. A medal that has survived the ruin of empires is no doubt a venerable relic, but it seems to have been struck but yesterday when compared with a shell or a leaf that has been buried millions of years ago in the drift of the primeval ocean, and now serves the geologist as a waymark through the past epochs of the earth’s history.

AMMONITES HENLEYI (MIDDLE LIAS).

If we examine the condition in which the fossils have been preserved in the strata successively deposited on the surface of our globe, we find that in general only parts of the original plant or animal have escaped destruction, and in these fragments also the primitive substance has often been replaced by other materials, so that only their form or their impression has triumphed over time. While soft and delicate textures have either been utterly swept away, or could only be preserved under the rarest circumstances (as, for instance, the insects and flowers inclosed in amber), a greater degree of hardness or solidity naturally gave a better chance of escaping destruction. Thus among plants the most frequent fossil-remains are furnished by stems, roots, branches, fruit-stones, leaves; and, among animals, by corals, shells, calcareous crusts, teeth, scales, and bones. But the few memorials that have thus survived the lapse of ages enable us to form some idea of the multitudes that have entirely perished; and the petrified shell of the Ammonite, or the jointed arms of the Encrinite, are proofs of the existence of the world of tiny beings which served them for their nourishment and have been utterly swept away. If we consider that the number of all the known species of fossil plants hardly amounts to 3,000, while the Flora of the present day, as far as it has been examined by systematical botanists, numbers at least 250,000 species; that the host of living insects is probably still more numerous, although not much more than 1,500 extinct species of this class are known to us; and that, finally, the remains of all the extinct crustaceous fishes, reptiles, and warm-blooded animals are far outnumbered by the species actually living—we may form some idea of the vast multitudes that have left no trace behind, and whose total loss will for ever confine within narrow limits our knowledge of the past phases of organic creation. This loss appears still greater when we consider the enormous extent of time during which the fossils known to us have successively existed, and that a part only of the comparatively small number of the orders, genera, and species to which they belong existed at one and the same epoch. But as, owing to the hard texture and mode of life which are so eminently favourable for the preservation of shells, we have been enabled to collect about 11,000 fossil species, a number not much inferior to that of the molluscs of the present day, we may justly conclude that the more perishable forms of life, of which, consequently, fewer vestiges have been preserved, were comparatively as numerous, and that ever since the first dawn of organic life our earth has borne an immense variety of plants and animals.

Though comparatively but few species have been preserved, yet sometimes the accumulation of fossil remains is truly astonishing. In the carboniferous strata we not seldom find more than one hundred beds of coal interstratified with sandstones, shales, and limestones, and extending for miles and miles in every direction. How luxuriant must have been the growth of the forests that could produce masses such as these, and what countless multitudes of herbivorous insects must have fed upon their foliage or afforded food to carnivorous hordes scarcely less numerous than themselves! The remains of corals, encrinites, and shells often form the greater part of whole mountain ranges, and, what is still more remarkable, mighty strata of limestone or flint are not seldom almost entirely composed of the aggregated remains of microscopical animals.

After these remarks on fossils in general, I will now briefly point out some of the most striking of the species so preserved to us as they successively appeared upon the stage of life.

In the Lower Laurentian Rocks, the most ancient strata known, only one fossil has hitherto been found. The Eozoon canadense, as it has been called, belonged to the Rhizopods, which occupy about the lowest grade in the scale of animal existence. Its massive skeletons, composed of innumerable cells, would seem to have extended themselves over submarine rocks, their base upwards of twelve inches in width and their thickness from four to six inches. Such is the antiquity of the Eozoon that the distance of time which separated it from the Trilobites of the Cambrian formation may be equal to the vast period which elapsed between these and the Tertiary ages. In other words, it is beyond our imagination to conceive.

TRILOBITE.

MAGNIFIED EYE OF TRILOBITE.

In the next following Cambrian formation we find, besides some zoophytes and shells, a number of Trilobites, which, however, appear to have been most abundant in the Silurian seas, where they probably swarmed as abundantly as the crabs and shrimps in the waters of the present age. Few fossils are more curious than these strange crustaceans, which so widely differ from their modern relatives. The jointed carapace is divided into three lobes, the middle prominent one forming the axis of the body, while the lateral ones were free appendages, under which the soft membranaceous swimming feet were concealed. Large eyes, resembling those of a dragon-fly, projected from the odd crescent-shaped head, and, being composed of many hundred spherical facets, commanded a wide view of the horizon. Provided with such complicated organs of vision, the helpless animal could betimes perceive the approaching enemy, or more easily espy its prey, consisting, most likely, of the smaller marine annelides or molluscs. From the structure of these remarkable eyes we may conclude that the waters of the old Cambrian or Silurian Ocean were as limpid as those of the present seas, and that the natural relations of light to the eye and of the eye to light cannot have greatly changed since that period. Many, if not all, of the Trilobites were capable of rolling themselves up into a ball, like wood-lice; and accordingly it is found that in many of them the contour of the head and tail is so constructed that they fit accurately when rolled up. Most probably the Trilobites either swam in an inverted position, the belly upwards, or crawled slowly along at the bottom of the shallow coast waters, where they lived gregariously in vast numbers.

PTERYGOTUS ACUMINATUS (EURYPTERID).

SPIRIFER PRINCEPS (BRACHIOPOD).

Contemporaneous with the Trilobites were the Eurypterids, which vary from one foot to five or six feet in length. One of the most striking characteristics of this remarkable order of crustaceans is the formidable pair of pincers with which they were armed. As their whole structure shows them to have been active swimmers, they must have made considerable havoc among the smaller fry of the Devonian and Silurian seas.

Then also abounded in hundreds of species the Brachiopods, a class of molluscs now but feebly represented by a scanty remnant. The greater part of the interior of the shell, consisting of two unequal valves, is occupied with branching arms, furnished with cilia, which cause a constant current to flow towards the mouth of the mollusc, and thus provide for its nourishment. The arms, as in the family of the Spiriferidæ, are sometimes supported by calcareous skeletons, arranged like loops or spirals.

Some Brachiopods are attached to stones, like oysters; in others the larger valve is perforated, and a sinewy kind of foot, passing through the aperture, serves as a holdfast to the animal.

Most of these helpless creatures did not survive the Carboniferous period, but the Terebratulæ, which still have their representatives in the modern seas, existed even then, so that their genealogical tree may justly boast of a very high antiquity.

The fishes, of which the oldest known specimen has been found in the Upper Silurian group (Lower Ludlow), become more frequent in the next following Devonian epoch, where they appear in a variety of wonderful forms, widely different from those of the present day. While in nearly all the existing fishes the scales are flexible, and generally either of a more or less circular form (cycloid), as in the salmon, herring, roach, &c., or provided with comb-like teeth, projecting from the posterior margin (ctenoid), as in the sole or perch, the fishes of the Devonian, Permian, and Carboniferous periods were decked with hard bony scales, either covered with a brilliant enamel, as in our sturgeons (ganoid), and arranged in regular rows, the posterior edges of each slightly overlapping the anterior ones of the next, or irregular in their shape, and separately imbedded in the skin (placoid), as in the sharks and rays of the present day. With rare exceptions their skeleton was cartilaginous; but the less perfect ossification of their bones was amply compensated by the solid texture of their enamelled coat of mail, which afforded them a better protection against enemies and injuries from without than is possessed by any bony-skeletoned fish of our days. They were, in fact, comparatively as well prepared for a hostile encounter as an ancient knight in armour, or as one of our modern iron-plated war ships. One of the most remarkable of these mail-clad Ganoids was the Pterichthys Milleri of the Old Red Sandstone of Scotland. In most of our fishes the pectoral fins are but weakly developed; here they constitute real arms, moved by strong muscles, and resembling the paddle of the turtle.

PTERICHTHYS MILLERI—RESTORED. (OLD RED SANDSTONE OF SCOTLAND.)

Besides the enormous masses of vegetable matter which distinguish the Carboniferous period, the stone beds of that formation likewise contain a vast number of animal remains. From the reptiles and fishes down to the corals and sponges, many new families, genera, and species crowd upon the scene, while many of the previously flourishing races have either entirely disappeared, or are evidently declining. Thus the Trilobites, formerly so numerous, are reduced to a few species in the Carboniferous period, and vanish towards its close.

In 1847 the oldest known reptiles were found in the coal field of Saarbrück, in the centre of spheroidal concretions of clay iron-stone, which not only faithfully preserved the skulls, teeth, and the greater portions of the skeletons of these ancient lizards, but even a large part of their skin, consisting of long, narrow, wedge-shaped, tile-like, and horny scales, arranged in rows. What a lesson for human pride! The pyramid of the Pharaoh Cheops, reared by the labour of thousands of slaves, has been unable to preserve his remains from spoliation even for the short space of a few thousand years, and here a vile reptile has been safely imbedded in a sarcophagus of iron ore during the vast period of many geological formations.

Still more recently (1854) other wonders have been brought to light in the clay iron-stone of Saarbrück. The wing of a grasshopper, with all its nerves as distinctly marked as if the creature had been hopping about but yesterday, some white ants or termites (now confined to the warmer regions of the globe), a beetle, and several cockroaches, give us some idea of the insects that lived at the time when our coal-beds were forming. Another highly interesting circumstance, relating to the fossils of that distant period, is that in several of them the patterns of their colouring have been preserved. Thus Terebratula hastata often retains the marks of the original coloured stripes which ornamented the living shell. In Aviculopecten sublobatus dark stripes alternate with a light ground, and wavy blotches are displayed in Pleurotomaria carinata. From these facts Professor Forbes inferred that the depth of the seas in which the Mountain Limestone was formed did not exceed fifty fathoms, as in the existing seas the Testacea, which have shells and well-defined patterns, rarely inhabit a greater depth.

The Magnesian Limestone or Permian group is remarkable chiefly for the vast number of fishes that have been found in some of its members, such as the marl slate of Durham and the Kupferschiefer, or copper slate, of Thuringia. From the curved form of their impressions, as if they had been spasmodically contracted, the fossil fish of the latter locality are supposed to have perished by a sudden death before they sank down into the mud in which they were entombed. Probably the copper which impregnates the stratum in which they occur is connected with this phenomenon. Mighty volcanic eruptions corrupted the water with poisonous metallic salts, and destroyed in a short time whole legions of its finny inhabitants.

VENTRICULITES—FOSSIL SPONGE (CHALK).

From the earliest ages the corals play a conspicuous part in fossil history; and as in our days we find them encircling islands and fringing continents with huge ramparts of limestone, so many an ancient reef, now far inland, and raised several thousand feet above the level of the sea, bears witness to the vast terrestrial changes that have taken place since it was first piled up by the growth of countless zoophytes.

SIPHONIA COSTATA—FOSSIL SPONGE (GREEN SAND, WARMINSTER).

With regard to the dimensions of the fossil corals we do not find that any of them exceeded in size their modern relatives; but their construction was widely different.

The fossil sponges of the primitive seas are likewise very unlike those of the present day.

Thus in all the ancient strata we find abundant spongidæ with a stony skeleton, while all the modern sponges possess a horny frame. The Petrospongidæ, or stone sponges, which have long since disappeared, are frequently shapeless masses; but a large number are cup-shaped, with a central tubular cavity, lined, as well as the outer surface, with pores more or less regularly arranged.

ENCRINUS LILIIFORMIS.
(Muschelkalk, Germany.)

PENTACRINUS BRIAREUS.

The Crinoids, or Sea-lilies, now almost entirely extinct, were extremely common in the primeval seas. Unlike our modern sea-stars, to which they are allies, they did not move about freely from place to place, but were affixed, like flowers, to a slender flexible stalk, composed of numerous calcareous joints connected together by a fleshy coat. The Carboniferous Mountain Limestone is loaded with their remains, and the Encrinus liliiformis is one of the leading fossils of the Muschelkalk of the Triassic group. The Pentacrinus briareus is of more modern date, and occurs in tangled masses, forming thin beds of considerable extent in the Lower Lias. This beautiful Crinoid, with its innumerable tentacular arms, appears to have been frequently attached to the drift wood of the Liassic sea, like the floating barnacles of the present day. In the still more recent Chalk group is found a remarkable form of star-fish, the Marsupites ornatus, which resembles in all respects the Crinoids, except that it is not and never was provided with a stem. It seems to have been rolled lazily to and fro, by the influence of the waves, at the bottom of the sea, and to have been anchored in its place by the action of gravity alone.

MARSUPITES ORNATUS. CHALK.

Of all the changes that have taken place in organic life, none perhaps are more remarkable than the transformations which the Cephalopod molluscs have undergone during the various geological eras. In the more ancient Palæozoic seas flourished the Orthoceratites, or straight-chambered shells, resembling a nautilus uncoiled. In the Carboniferous ages the Goniatites acquired their highest development. These shells were spirally wound, having the lobes of the chambers free from lateral denticulations or crenatures, so as to form continuous and uninterrupted outlines.

Both Orthoceratites and Goniatites disappear in the Triassic times, and are replaced by hosts of Ammonites, which successively flourished in more than 600 species, and are characterised by an external siphon and chambers of complicated, often foliated, pattern. This foliated structure gives a remarkable character to the intersection of the chamber partitions with the shell, and must have added greatly to the strength of the shell, which was always delicate and often very beautiful. The Ammonites, which made their first appearance towards the end of the Triassic period, abounded in the Oolitic and Cretaceous periods, and were replaced by new forms before the Tertiary beds were deposited. Among these we find the Ancyloceras gigas, which may be regarded as an Ammonite partially unrolled, and the Turrilites tuberculatus, which has the form and peculiar symmetry of a univalve shell.

TURRILITES TUBERCULATUS.

RESTORED BELEMNITE.

In several of the older rocks, especially the Lias and Oolite, Belemnites are frequently met with. These singular dart- or arrow-shaped fossils were supposed by the ancients to be the thunderbolts of Jove, but are now known to be the petrified internal bones of a race of voracious cuttle-fishes, whose importance in the Oolitic or Cretaceous Seas may be judged of by the frequency of their remains and the 120 species that have been hitherto discovered.

Belemnites two feet long have been found, so that, to judge by analogies, the animals to which they belonged as cuttle-bones must have measured eighteen or twenty feet from end to end. Provided with prehensile hooks on their long arms, and with a formidable parrot-like bill, these huge creatures must have proved most dangerous antagonists, even to the well-protected fishes that lived in the same seas. But of all the denizens of the Mesozoic Ocean none were more powerful than the large marine or enaliosaurian reptiles, which, flourishing throughout the whole of the Triassic period, were lords of all they surveyed down to the end of the Cretaceous epoch. First among these monsters appears the gigantic Ichthyosaurus, which has been found no less than forty feet long—a creature half fish, half lizard, and combining, in strange juxtaposition, the snout of the porpoise, the teeth of the crocodile, and the paddles of the whale. But the most remarkable of its features is the eye, surpassing a man’s head in size, and wonderfully adapted for vision both far and near.

ICHTHYOSAURUS COMMUNIS.

PLESIOSAURUS DOLICHODEIRUS.
(British Museum—Found in the Lias of Street, near
Glastonbury.)

In the quarries of Caen in Normandy, at Lyme Regis in Dorsetshire, and particularly at Kloster Banz in Franconia, where the largest known specimen has been discovered, entire skeletons of the formidable Ichthyosaurus have been exhumed from the Liassic shale—memorials of the ages long since past, when lands now far removed from the ocean still lay at the bottom of the sea, and formed the domain of gigantic lizards. The enormous jaw-bones of the Ichthyosauri, which in the full-grown animal could be opened seven feet wide, were armed along their whole length with powerful conical teeth, showing them to have been carnivorous, and the half-digested remains of fishes and reptiles found within their skeletons indicate the precise nature of their food. The size of the swallowed object proves also that the cavity of the stomach must have corresponded with the wide opening of the jaws. Thus powerfully equipped for offensive warfare; excellent swimmers from their compressed cuneiform trunk, their long broad paddles, and their stout vertical tail-fin; provided, moreover, with eyes capable of piercing the dim light of the ocean depths, they must have been formidable indeed to the contemporaneous fishes.

The Ichthyosaurus was admirably formed for cleaving the waves of an agitated sea; but the Plesiosaurus was equally well organised for pursuing its prey in shallow creeks and bays defended from heavy breakers. Its long swan-like neck no doubt enabled it to drag many a victim from its hiding-place. While these huge lizards were the terror of the seas, the Pterodactyles, a race of winged lizards, armed with long jaws and sharp teeth, hovered in the air. With the exception of the greatly elongated fifth finger, to which, as well as to the whole length of the arm and body, the membranous wing or organ of flight was attached, the fingers of this strange animal were provided with sharp claws, so that it was probably enabled, like the bat, to suspend itself from precipitous rock-walls.

It is a remarkable fact, that, whereas the Pterodactyles of the older Lias beds did not exceed ten or twelve inches in length, the later forms, found fossil in the Greensand and Wealden beds of the Lower Cretaceous formation, must have been at least 16½ feet long. That these reptiles were not the only vertebrated animals capable of hovering in the air at the time when the huge Ichthyosaurus was lord of the seas, is proved by a bird about the size of a rook, which was discovered in 1862, in the lithographic slate of Solenhofen in Bavaria, a stone-bed belonging to the period of the Upper Oolite. The skeleton of this valuable specimen, now in the British Museum, is almost entire, with the exception of the head, and retains even its feathers. Still older fossil mammalia have been found near Stuttgard, in the uppermost bed of the Triassic deposits, and in the Lower Oolite of Oxfordshire. These interesting remains, which carry back the existence of the mammals to a very remote period, belong to small marsupial, or opossum-like, animals. The jaws, which are the principal parts preserved, are exceedingly minute, and remarkable for the number and distribution of their teeth, which prove them to have been either insectivorous or rodent.

The remains of the Ichthyosauri and Plesiosauri occur chiefly in the Liassic group, but the more recent Cretaceous (Wealden) formation is distinguished by the presence of still more enormous land saurians. On their massive legs and unwieldy feet these monsters stood much higher than any reptile of our days, and resembled in bulk and stature the elephants of the present world.

The carnivorous Megalosaurus (for its sharply serrated teeth indicate this mode of life) appears to have preceded the gigantic Iguanodon, whose dentition denotes a vegetable food. Like the giant sloths of South America—the Megatherium and the Mylodon—the Iguanodon was provided with a long prehensile tongue and fleshy lips to seize the leaves and branches on which it fed. Professor Owen estimates its probable length at between fifty and sixty feet, and to judge by the proportions of its extremities, and particularly of its huge feet, it must have exceeded the bulk of the elephant eightfold.

During the following Upper Cretaceous epoch flourished the Mosasaurus, a marine saurian, first discovered in the quarries of St. Peter’s Mount, near Maestricht,[^[1]] and supposed to have been twenty-four feet in length. But the supremacy of the reptiles was now drawing to its close, and in the Tertiary period we at length see the Mammalia assume a prominent place on the scene of life. The oldest of these tertiary quadrupeds differ so widely from those of the present day as to form distinct genera. The Palæotheriums, for instance, of which there are seventeen species, varying in dimensions from the size of a rhinoceros to that of a hog, combine in their skeleton many of the characters of the tapir, the rhinoceros, and the horse, while the Anoplotheriums, whose size varied from that of a hare to that of a dwarf ass, resembled in some respects the rhinoceros and the horse, and in others the hippopotamus, the hog, and the camel.

In the Miocene epoch many of these more ancient quadrupeds no longer appear upon the scene, while others still flourish in its upper period along with still existing genera, and with forms long since extinct, such as the Dinotherium. This huge animal is particularly remarkable for its two large and heavy tusks, placed at the extremity of the lower jaw, and curved downwards like those in the upper jaw of the walrus. It was formerly supposed to be an herbivorous cretacean, and to have used its anterior limbs principally in the act of digging for roots. The remains on which these speculations were founded were the huge jaws and shoulder-blade discovered at Epplesheim in Hesse Darmstadt; but an immense pelvis of the animal, measuring six feet in breadth and four and a quarter feet in height, discovered by Father Sanno Solaro, in the department of the Haute Garonne, proves that this supposed aquatic pachyderm was a gigantic marsupial, and that the dependent trunks of the unwieldy animal, instead of serving the purpose of anchoring it to the banks of rivers, answered the more homely, but equally important office, of lifting the young into the maternal pouch. ‘The remarkable history of the successive discovery of its bones,’ says Professor Haughton, ‘and the change of views consequent thereupon, should teach geologists modesty in the expression of their opinion.’ During this period also flourished in India, along with many other strange forms of life, the Colossochelys Atlas, a tortoise of the most gigantic proportions, measuring, probably, nearly twenty feet on the curve of the carapace, and dwarfing into insignificance the great Indian tortoise of the present day.

The nearer we approach our own times, the greater becomes the proportion of still existing genera and species; and it is remarkable that as early as the Pliocene epoch we find a geographical distribution of mammalian life analogous to that which now characterises the various regions of the earth.

Thus the fossil monkeys of South America have the nostrils wide apart like all the existing simiæ of the new world, and fossil monkeys with approximated nostrils, the characteristic mark of all the old world quadrumana, are exclusively found in Asia and in Europe, where now a small species of monkey is confined to the Rock of Gibraltar, but where, in the Upper Miocene times, large long-armed apes, equalling man in stature, lived in the oak forests of France. Thus also South America, where alone sloths and armadilloes exist at the present day, is the only part of the world where, in the younger tertiary rocks, the remains of analogous mammals—the Megatherium, the Mylodon, and the Glyptodon—have been found.

The Mylodon was a colossal sloth, eleven feet long and with a corresponding girth. When we consider the huge size of the pelvis and the massiveness of the limbs, we must needs conclude that Professor Owen could not possibly have given the unwieldy animal a more appropriate surname than that of robustus.

The Megatherium was of still larger size. Its length was as much as eighteen feet, the breadth of its pelvis was six feet, and the tail, where it was attached to the body, must have measured six feet in circumference. The thigh bone was nearly three times as great as that of the largest known elephant, the bones of the instep and those of the foot being also of corresponding size. The general proportions both of the Megatherium and Mylodon resembled those of the elephant, the body being relatively as large, the legs shorter and thicker, and the neck very little longer. The Megatherium may have had a short proboscis, but the Mylodon exhibits no mark of such contrivance.

It is evident, from the bulk and construction of these huge animals, that they did not, like the sloths of the present day, crawl along the under side of the boughs till they had reached a commodious feeding place, but that, firmly seated on the strong tripod of their two hind legs and powerful tail, they uprooted trees or wrenched off branches with their fore limbs, which were well adapted for grasping the trunk or larger branches of a tree. The long and powerful claws were also, no doubt, useful in the preliminary process of scratching away the soil from the roots of the trees to be prostrated. This task accomplished, the long and curved fore claws would next be applied to the opposite sides of the loosened trunk. ‘The tree being thus partly undermined and firmly grappled with, the muscles of the trunk, the pelvis, and hind limbs, animated by the nervous influence of the unusually large spinal cord, would combine their forces with those of the anterior members in the efforts at prostration. If now we picture to ourselves the massive frame of the Megatherium, convulsed with the mighty wrestling, every vibrating fibre reacting upon its bony attachment with a force which the sharp and strong crests and apophyses loudly bespeak, we may suppose that that tree must have been strong indeed which, rocked to and fro, to right and left, in such an embrace, could long withstand the efforts of its ponderous assailant.’

GLYPTODON CLAVIPES.

The Glyptodon, a colossal armadillo of the size of an ox, was covered with a thick heavy tessellated bony armour, which, when detached from the body, resembled the section of a large cask. This harness measured on its curve from head to tail at least six feet, and four feet from side to side, so that a Laplander might have squatted comfortably under its roof.

In the superficial deposits of diluvial drift, in Germany and England, in Italy and Spain, in Northern Asia as well as in North America, between the latitudes of 40° and 75°, the bones of the large extinct Pachyderms have been found, and become more and more abundant as we approach the ice-bound regions within the Arctic Circle. The Siberian tundras, and the islands in the Polar Sea beyond, are, above all, so rich in the fossil remains of the Mammoth, or primitive elephant, that its tusks form a not unimportant branch of commerce. From the presence of so large an animal in treeless wilds, where now only small rodents or their persecutors, the Arctic fox and snow owl, find the means of subsistence, it has been inferred that Siberia must in those times have enjoyed a tropical climate; but many weighty arguments have been arrayed against this opinion. The musk-ox, it is well known, prefers the stinted herbage of the Arctic regions, while the allied buffalo can only thrive in a warm country, and different species of bears are found in all zones; so also the primitive elephant was formed for a temperate or cold climate. Instead of being naked, like his living Asiatic and African relations, the Mammoth was covered with a warm clothing, well fitted to brave a low temperature, a fact sufficiently proved by the carcass of one of these animals which was found, in the year 1803, imbedded in a mass of ice on the bank of the Lena in latitude 70°. Its skin was covered first with black bristles, thicker than horse-hair, from twelve to sixteen inches in length, secondly with hair of a reddish-brown colour, about four inches long, and thirdly with wool of the same colour as the hair, about an inch in length.

The discoveries of Middendorff on the banks of the Taymur likewise show that in those times the climate of Siberia was by no means tropical, for in latitude 75° 15′ he found the trunk of a larch imbedded with the bones of a Mammoth in an alluvial stratum fifteen feet above the level of the sea. Fragments of pine leaves have likewise been extracted from cavities in the molar teeth of a fossil rhinoceros, discovered on the banks of the Wiljui, in latitude 64°. The numerous land and freshwater shells accompanying the Mammoth in the highest latitudes are also, almost without exception, identical with those now existing in Siberia.

The Mastodon, though not uncommon among the fossils of the old world, is more abundantly found in North America. The molar teeth of this huge animal, whose grinding surfaces had their crowns studded with conical eminences, more or less resembling the teats of a cow, differed greatly from the flat-crowned grinders of the Mammoth; but both had twenty ribs like the living elephant, and must have been similar in size and general appearance. The body of the Mastodon would seem to have been longer, its limbs thicker and shorter, and, perhaps, its form, on the whole, rather approaching that of the hippopotamus, which it probably resembled also in some of its habits. Its mouth was broader than that of the elephant, and although it was certainly provided with a long trunk, it must have lived on soft succulent food, and it seems to have rarely left the marshes and muddy ponds, in which it would find ample food.

The most complete, and probably the largest, specimen of the Mastodon ever found was exhumed in 1845, in the town of Newbury, New York, the length of the skeleton being twenty-five feet, and its height twelve feet. From another specimen, found in the same year, in Warren County, New Jersey, the clay in the interior within the ribs, just where the contents of the stomach might naturally have been looked for, furnished some bushels of vegetable substance. A microscopic examination proved this matter to consist of pieces of small twigs of a coniferous tree of the cypress family, probably the young shoots of the white cedar (Thuja occidentalis) which is still a native of North America.

This interesting discovery likewise proves that the climate of North America was then, like that of Siberia, not very different from that of the present day.

The most remarkable of the fossil Ruminants are found among the deer tribe. The largest of these is the Sivatherium giganteum, discovered in the Tertiary beds of the sub-Himalayan hills. It was a deer with four horns, and, to judge by the size of its bones, must have exceeded the elephant in its dimensions. Near this huge ‘antlered monarch of the waste’ the extinct Cervus megaceros, found in the bogs and shallow marls of Ireland, appears as a mere dwarf, in spite of its large branching palmate horns, often weighing eighty pounds, and a corresponding stature far exceeding that of our modern deer.

The colossal size of many of the extinct plants and animals might seem to favour the belief that organic life has degenerated from its former powers; but a survey of existing creation soon proves the vital principle to be as strong and flourishing as ever.

No fossil tree has yet been found to equal the towering height of the huge Sequoias and Wellingtonias of California; and though the Horsetails and Clubmosses of the Carboniferous ages may well be called colossal when compared with their diminutive representatives of the present day, yet their height by no means exceeded that of the tall bamboo of India. No fossil bivalve is as large as the Tridacna of the tropical seas; and though our nautilus is a mere pigmy when compared with many of the Ammonites, our naked cuttlefishes are probably as bulky as those of any of the former geological formations. The living crustaceans and fishes are not inferior to their predecessors in size, and though the giant saurians of the past were much larger than our crocodiles, yet they do not completely dwarf them by comparison. The extinct Dinornis[^[2]] far surpassed the ostrich in size, but the Mammoth and the Mastodon find their equal in our elephant; and though the sloths of the present day are mere pigmies when compared with the Megatherium, yet no extinct mammal attains the size of the Greenland whale.

The perfect preservation of so many fossil remains of animals and plants, which enables us to trace the progress of organic life on earth from one vast epoch to another, is surely wonderful enough; but we must consider it as a still greater wonder that phenomena usually so evanescent as foot-prints, ripple-marks, and rain-prints should in some cases have been permanently engraved in stone, and appear as distinct after millions of years as if their traces had been left but yesterday. All these marks were at first printed on soft argillaceous mud, on the sea-shore, or on the borders of lakes and rivers, which retained them as they became dry. Sand or clay having then been drifted into the mould by the wind, or deposited in its cavity by the next tide, a permanent cast was made, indented in the lower stratum and standing out in relief on the upper one.

Thus rain-drops on greenish slates of the Coal period, with several worm tracks, such as usually accompany rain-marks on the recent mud of modern beaches, have been discovered near Sydney, in Cape Breton. As the drops resemble in their average size those which now fall from the clouds, we may presume that the atmosphere of the Carboniferous period corresponded in density with that now investing the globe, and that different currents of air varied then as now in temperature, so as, by their mixture, to give rise to the condensation of aqueous vapour.

In like manner it has been possible to detect the footprints of reptiles, even in shales as old as the Cambrian formation, and to follow their trail as they walked or crawled along.

In the Upper New Red Sandstone (Lower Trias), near Hildburghausen, in Saxony, a strange unknown animal, supposed to belong to the frog order, has left foot-prints bearing a striking resemblance to the impressions made by a human hand; and in the still older red sandstone of Connecticut, a gigantic bird has marked a foot four times larger than that of the ostrich. It existed long before the Ichthyosaurus was seen on earth, and yet by a singular chance its traces, printed on a foundation proverbially unstable, have outlived the wreck of so many ages.

However brief and defective the foregoing review of the fossil world may have been, it has still sufficed to point out the existence on our planet of so many habitable surfaces, each distinct in time, and peopled with its peculiar races of aquatic and terrestrial beings, all admirably fitted for the new states of the globe as they arose, or they would not have increased and multiplied and endured for indefinite periods.

‘The proofs now accumulated,’ says Sir Charles Lyell, ‘of the close analogy between extinct and recent species are such as to leave no doubt on the mind that the same harmony of parts and beauty of contrivance which we admire in the living creation has equally characterised the organic world at remote periods. Thus, as we increase our knowledge of the inexhaustible variety displayed in living nature, our admiration is multiplied by the reflection that it is only the last of a great series of pre-existing creations, of which we cannot estimate the number or limit in times past.’

CHAPTER III.
SUBTERRANEAN HEAT.

Zone of invariable Temperature—Increasing Temperature of the Earth at a greater Depth—Proofs found in Mines and Artesian Wells, in Hot Springs and Volcanic Eruptions—The whole Earth probably at one time a fluid mass.

Born neither to soar into the air, nor to inhabit the deep waters, nor to pass his life in subterranean darkness, man is unable to depart to any considerable distance from the earth’s surface. If he ascends in a balloon, he soon reaches the limits where the rarefied atmosphere renders breathing impossible; a few thousand feet limit his efforts to pierce the earth’s crust; and should he be cast out into the sea, he is soon drowned. But beyond the limits to which his body is confined, his mind soars into space, and plunging into the unknown interior of our globe, seeks to unravel the mystery of its formation. In the following pages I purpose briefly to point out the circumstances which guide him in his speculations, and enable him to roam, at least in spirit, through the profound abysses of the subterranean world.

As we all know, the temperature of the atmosphere soon communicates its changes to the surface of the earth; and our meadows, which when warmed by the rays of the sun are green and covered with flowers, harden in winter into a lifeless plain. But the influence of the sun’s heat upon the soil is merely superficial, so that in the temperate zones the annual fluctuations of the thermometer are no longer perceptible at a depth of from 60 to 80 feet.

Thus, in the cellars of the Parisian observatory, a thermometer, placed many years ago 86 feet below the surface, invariably indicates +11°7 Celsius; the summer above may be ever so intensely hot, or the winter ever so cold, the column of mercury never deviates a hair’s breadth from the height it has once attained. Below these limits the warmth of the earth gradually increases—a fact placed beyond all doubt by the innumerable observations that have been made in mines, and during the boring of Artesian wells. For wherever sinkings have been made, a rising of the thermometer has always been found to take place as the auger penetrates to a greater depth below the surface. Thus, to cite but a few examples, the temperature of the Artesian well of Grenelle in Paris, which, at a depth of 917 French feet, amounted to +22°2 C., increased at the depth of 1,555 feet to +26°43, and the water, which now gashes forth from the depth of 1,684 feet, constantly maintains the same lukewarm temperature of +27°70.

During the boring of the well of Neusalzwerk, in Westphalia, the temperature rose at the various depths of 580, 1,285, and 1,935 feet from +19°7 C. to +27°5 and +31°4, until, finally, when the depth of 2,144 feet was attained, the saline spring issued forth with a constant temperature of +33°6. As from the experience acquired in mines and Artesian wells, the temperature is found to increase by one degree for about every successive 80 or 100 feet, the internal warmth of the earth, supposing it to increase in the same proportion towards the centre, would, at the depth of 10,000 feet, be equal to that of boiling water, and at that of 80 or 100 miles sufficiently great to melt the hardest rock.

Whether this steady increase really takes place is of course only matter of conjecture; but the history of hot springs and volcanic eruptions shows us that everywhere a very high degree of heat exists at considerable depths below the surface.

Most springs in the temperate zone, without being warm in a remarkable degree, still possess a higher temperature than the average warmth of the air in the locality where they gush forth, while in the tropical zone they are frequently cooler—a proof that in both cases they issue from a depth independent of the fluctuating atmospherical influences of the surface. While these cool or cold springs, spread in immense numbers over the earth, attest the existence everywhere of a subterranean source of heat, the warm and hot springs remind us of its intensity at more considerable depths. These thermal sources are confined to no climate, for in the cold land of the Tschuktschi, where the soil must be perpetually frozen to a depth of several hundred feet, boiling water is found to gush forth, as well as in the tropical Feejee Islands.

The hot springs, though of frequent occurrence in all parts of the world, are not the only or principal vents of subterranean heat. Far greater quantities of caloric are constantly pouring forth from the numerous volcanoes and solfataras, which are likewise distributed all over the surface of the globe. The violent convulsions which attend every outflow of lava are proofs that these torrents of liquid stone must have been forced upwards from a far greater depth than the water of the hot springs. The temperature necessary for their production likewise points to this fact, for to melt stones a heat of at least 2,000°C. is required. But volcanoes, like hot springs, are found in every zone; beyond the Arctic Circle, as well as in the most southern land attained by Sir James Ross in his memorable voyage. They line the coasts of the Pacific, as well as those of the Sea of Kamtschatka. They desolate Iceland, as they devoured Pompeii and Herculaneum; and everywhere they pour forth the same masses of fluid stone; so that the geologist is not able to distinguish the lavas of the Andes chain from those of Etna or Vesuvius. But phenomena so much alike in character, common to all parts of the globe, can hardly be dependent upon mere local circumstances, and speak loudly in favour of the theory which supposes our earth to have been at one time a ball of liquid fire. Wandering through space during a course of unnumbered ages, this huge mass of molten stones and metals gradually cooled, and at length got covered with a solid crust, below which the ancient furnaces are still burning, and striving to burst their fetters. Well may we say with Horace—

‘Incedimus per ignes

Suppositos cineri doloso.’

CHAPTER IV.
SUBTERRANEAN UPHEAVALS AND DEPRESSIONS.

Oscillations of the Earth’s Surface taking place in the present day—First ascertained in Sweden—Examples of Contemporaneous Upheaval and Depression in France and England—Probable Causes of the Phenomenon.

While the sea and the atmospheric ocean are subject to perpetual fluctuations, and the poet justly compares the uncertain tenure of human prosperity with the restless wave or the inconstant wind, the solid earth is generally regarded as the emblem of stability. But an examination of the various strata of aqueous origin which constitute by far the greater part of the actual dry land soon shows the fallacy of this opinion.

The fossils of marine origin which occur in so many of our oldest rocks, now situated far above the level of the ocean, must necessarily have been raised from the deep. On the towering Andes, fifteen thousand feet above the tide-marks of the Pacific, the geologist finds sea-shells imbedded in the rock, and high above the snow-line the chamois-hunter of the Alps wonders at the sight of spirally-wound Ammonites that once enjoyed life at the bottom of the Liassic Sea. In strata of a more modern date, we find, on the banks of the river Senegal, far inland, large deposits of the Arca senilis, a mollusc still living on the neighbouring coast. On the borders of Loch Lomond, twenty feet above the level of the sea, shells of the edible cockle and sea-urchin repose in a layer of brown clay, and the banks of the Forth and of the Clyde, thirty feet higher than the storm tides, inclose remains of common shells of the present period, such as the oyster, the mussel, and the limpet. Along the shores of the Mediterranean, at Monte Video and at Valparaiso, in the isles of the Pacific and at the Cape, in California and Haiti, we meet with similar instances of elevation, which, though geologically recent, may yet be of a sufficiently ancient date to have preceded the appearance of man on earth. But proofs are not wanting that the upheaving power which has wrought so many changes in the past is still actively employed in remodelling the surface of the earth.

This important geological fact was first ascertained on the coast of Sweden, where the peculiar configuration of the shore makes it easy to appreciate slight changes in the relative level of land and water. For the continent is fringed with countless rocky islands, called the ‘skär,’ within which boats and small vessels sail in smooth water even when the sea without is strongly agitated. But the navigation is very intricate, and the pilot must possess a perfect knowledge of the breadth and depth of every narrow channel, and the position of innumerable sunken rocks. On such a coast even a slight change of level could not fail to become known to the mariner, and to attract the attention of the learned, as soon as the book of nature began to be more accurately studied.

Early in the last century the Swedish naturalist Celsius collected numerous observations, all pointing to the fact of a slow elevation of the land. Rocks both on the shore of the Baltic and the German Ocean, known to have been once sunken reefs, were in his time above water; small islands in the Gulf of Bothnia had been joined to the continent, and old fishing grounds deserted, as being too shallow or entirely dried up. These changes of level, which he estimated at about three feet in a century, Celsius attributed to a sinking of the waters of the Baltic, owing possibly to the channel, by which it discharges its surplus waters into the Atlantic, having been gradually widened and deepened by the waves and currents. But the lowering of level would in that case have been uniform and universal over that inland sea, and the waters could not have sunk at Torneo while they retained their former level at Copenhagen, Wismar, Stralsund, and other towns which are now as close to the water’s edge as at the time of their foundation. Playfair (1802) and Leopold von Buch (1807) first attributed the change of level to the slow and insensible rising of the land, and the subsequent investigations of Sir Charles Lyell in 1834 have placed the fact beyond a doubt.

The attention of geologists having once been directed to the partial upheaval of the Scandinavian peninsula, similar facts were soon pointed out in other countries. At Bourgneuf, near La Rochelle, the remains of a ship wrecked on an oyster bank in the year 1752, now lie in a cultivated field, fifteen feet above the level of the sea; and, within a period of twenty-five years the parish has gained at least 1,500 acres, a very acceptable gift of the subterranean plutonic power. Port Bahaud, where formerly the Dutchmen used to take in cargoes of salt, is now 9,000 feet from the sea, and the Island of Olonne is at present surrounded only by swamps and meadows. These and similar phenomena, such as the constant rise of the chalk cliffs at Marennes, cannot possibly be explained by recent driftings, but evidently proceed from a slow upheaval of the coasts and the adjacent sea-bed.

On the opposite shores of the Atlantic, we find Newfoundland undergoing a similar process of elevation; for cliffs over which, thirty or forty years ago, schooners used to sail with perfect safety, are now quite close to the surface; and in the Pacific the depth of the channel leading to the port of Honolulu is gradually decreasing from the same cause.

While many coasts thus show signs of progressive elevation, others afford no less striking proofs of subsidence, frequently in close proximity to regions of upheaval.

Thus on the south-west coast of England, in Cornwall, Devon, and Somerset, submarine forests, consisting of the species still flourishing in the neighbourhood, are of such frequent occurrence that, according to Sir Henry de la Beche, ‘it is difficult not to find traces of them at the mouths of all the numerous valleys which open upon the sea.’ Sometimes they are covered with mud or sand, and generally the roots are found in the situation where they originally grew, while the trunks have been horizontally levelled. At Bann Bridge, specimens of ancient Roman pottery have been discovered twelve feet below the level of the sea, and the remains of an old Roman road, now submerged six feet deep, prove that the subsidence of the land has been going on since the times of Julius Cæsar and Agricola.

On the east coast the phenomenon is still more striking, particularly in the Wash, that shallow bay between Lincolnshire and Norfolk on whose opposite shores a submarine forest extends, the trunks and stubbles of which become apparent at ebb-tide. On the coasts of Normandy and Brittany we likewise find traces of depression, pointing to some future time when perhaps many a bluff headland, now boldly fronting the ocean, may have disappeared beneath the waves.

Huts of the Esquimaux and of the early Danish colonists on the coast of Greenland, now submerged at high tide, could not possibly have been originally constructed in so inconvenient a situation; and at Puynipet, in the South Sea, habitations sunk beneath the water likewise prove a gradual subsidence of the land.

On many coasts and islands modern scientific explorers have hewn marks in the rock, to enable future generations to judge of the changes which are slowly but surely altering the configuration of the land and tracing new boundaries to the ocean. Had our forefathers left us similar memorials, we should know much more about the oscillatory movements of the earth-rind than we know now; but, unfortunately, experimental natural philosophy is but of recent date, and the marks chiselled out upon the Swedish rocks in the years 1731 and 1752 are the earliest records by which the chronological progress of elevation or subsidence can be distinctly ascertained.

This phenomenon, which has played so important a part in the physical annals of our globe, having once been accurately determined, enables the geologist to explain many facts for which, before it became known, it was impossible to account.

We now need not wonder at seeing sea-shells imbedded in the highest mountains or buried hundreds of fathoms under the ground, at alternating layers of marine and sweet-water deposits being frequently storied one above the other, or at originally horizontal strata being now found at every possible angle of inclination.

The imperceptible slowness with which many of these vast changes are actually taking place warrants the inference that violent volcanic revolutions have no doubt been far less instrumental in moulding the earth-rind to its present form than the slow oscillatory movements of elevation and depression which from time immemorial have been constantly altering its surface.

The causes of these oscillatory movements are still very imperfectly known, though a probable hypothesis attributes them to the expansion by increased temperature of extensive deep-seated masses of matter. As the elevation of some tracts seems to coincide with the proportionate depression of others at a greater or less distance, these alternating upheavals and subsidences may possibly be the result rather of the lateral shifting of the flow of heat from one mass of subterranean matter to a neighbouring mass than of its positive increase on the whole. ‘Such a lateral diversion of the outward flow of heat,’ says Mr. Poulett Scrope, ‘we may presume to be caused by the deposition over certain areas of thick newly-formed beds of any matter imperfectly conducting heat, like sedimentary sands, gravels, clays, shales, or calcareous mud, by which the outward transmission of heat being checked, it must accumulate beneath, while a portion of it will pass off laterally to augment the temperature of mineral matter in neighbouring areas; just as the water of a spring, if its usual issue is blocked up, will accumulate in the fissures or pores of the rock containing it, until it finds a vent on either side and at a higher level. Owing to this increase, the resistance opposed by the overlying rocks in that quarter may be sooner or later overcome, and their elevation brought about, through the dilatation of the mineral matter beneath.’

CHAPTER V.
SUBTERRANEAN WATERS AND ARTESIAN WELLS.

Subterranean Distribution of the Waters—Admirable Provisions of Nature—Hydrostatic Laws regulating the Flow of Springs—Thermal Springs—Intermittent Springs—The Geysir—Bunsen’s Theory—Artesian Wells—Le Puits de Grenelle—Deep Borings—Various Uses of Artesian Wells—Artesian Wells in Venice and in the Desert of Sahara.

In every zone the evaporating power of the sun raises from the surface of the ocean vapours, which hover in the air until, condensed by cold, they descend in rain upon the earth. Here part of them are soon restored to the sea by the swollen rivers; another part is once more volatilised; but by far the larger quantity finds its slow way into the bowels of the earth, where it serves for the perennial supply of wells and springs.

The distribution of these subterranean waters, and the simple laws which regulate their circulation, afford us one of the most interesting glimpses into the physical economy of our globe. We know that the greater part of the earth’s surface is composed of stratified rocks, or alternate beds of impermeable clay and porous limestone or sand, which were originally deposited in horizontal layers, but have since been more or less displaced and set on edge by upheaving forces. Wherever permeable beds of limestone or sand crop out on the surface of the land, the residuary portions of rain-water which are not disposed of by floods or by evaporation, must necessarily penetrate into the pores and fissures, and descend lower and lower, until they finally reach an impermeable stratum which forbids their further progress to a greater depth.

The granite, gneiss, porphyry, lava, and other unstratified and crystalline rocks of igneous origin, which cover about a third part of the habitable globe, are likewise intersected by innumerable fissures and interstices, which, in a similar manner, collect and transmit rain-water.

Thus the plutonic or volcanic forces which have gradually moulded the dry land into its present form have also provided it with the necessary filters, drains, reservoirs, and conduits, for the constant replenishment of springs, brooks, and rivers. As every porous layer is more or less saturated with moisture, the stratified rocks are frequently traversed at various depths by distinct sheets of water, or rather, in most cases, by permanently drenched or waterlogged sheets of chalk or sand. Thus, in a boring undertaken in search of coal at St. Nicolas d’Aliermont, near Dieppe, no less than seven very abundant aquiferous layers or beds of stone were met with from about 75 to 1,000 feet below the surface. In an Artesian boring at Paris, five distinct sheets of water, each of them capable of ascension, were ascertained; and similar perforations executed in the United States, and other countries, have in the same manner traversed successive stages of aqueous deposits.

Thus there can be no doubt that vast quantities of water are everywhere accumulated in the porous strata of which a great part of the superficial earth-rind is composed, the rapidity with which they circulate varying of course with the amount of hydrostatic pressure to which they are subjected, and the more or less porous and permeable nature of the beds through which they percolate. Were the ground we stand on composed of transparent crystal, and the subterranean water-courses tinged with some vivid colour, we should then see the upper earth-crust traversed in every direction by aqueous veins, and frequently as saturated with water as the internal parts of our body are with blood. But Nature not only perennially feeds our springs and brooks from the inexhaustible fountains of the deep; it is also one of her infinitely wise provisions that the same water which, if placed in casks or open tanks, becomes putrid, continues fresh so long as it remains in the cavities and interstices of the terrestrial strata. While filtering through the earth, it is generally cleansed of all the organic substances whose decay would inevitably taint its purity, and comes forth salubrious and refreshing, a source of health and enjoyment to the whole animal creation.

The extreme limits to which the waters descend into the earth of course escape our direct observation, as the lowest point to which the subterranean regions have been probed is less than 2,000 or 2,500 feet below the level of the sea; but as we know from the formation of many basins that the strata of which they are composed attain in many cases a thickness of from 20,000 to 30,000 feet, there can hardly be a doubt that they are permeated by water to an equal depth.

As steam plays so great a part in volcanic phenomena, the seat or effective cause of which must needs be sought for at an immense distance below the surface of the earth, we have another proof of the vast depth to which the subterranean migrations of water are able to attain.

After this brief glimpse into the reservoirs of the deep, we have to ascertain the power which raises their liquid contents and forces them to reappear upon the surface of the earth. If we pour water into a tube, bent in the form of the letter U, it will rise to an equal level in both branches. We will now suppose that the left branch of the tube opens at the top into a vast reservoir, which is able to keep it constantly filled, and that the right branch is cut off near the bottom, so that only a small vertical piece remains. The pressure of the water column in the left branch will in this case force the liquid to gush out of the orifice of the shortened right branch to the level which it occupied while the branch was still entire.

These two hydrostatic laws, or rather these two modifications of the same law, have been frequently put to practical uses, as, for instance, in the communicating tubes which distribute the waters of an elevated source or reservoir to the various districts of a town, or in the subterranean conduits which serve to create fountains, such as those of Versailles or the Crystal Palace.

When the Romans intended to lead water from one hill to another, they constructed, at a vast expense, magnificent aqueducts across the intermediate valley; but the Turks, whom we look upon as ignorant barbarians, obtain the same result in a much more economical manner, and in this respect far surpass the ancients, who, had they been better acquainted with the first principles of hydrostatics, would indeed have left us fewer specimens of their architectural skill, but would at the same time have saved themselves a great deal of unnecessary expense.

Down the slope of the hill from which the water is to be conducted, the Turks lay a tube of brick or metal, which, crossing the valley, moulds itself to its different inflections, and ultimately ascends the declivity of the hill on the opposite side, where, in virtue of the law above cited, the water rises as high as on that from which it descended. If we suppose the descending branch of the tube to be prolonged only as far as the level of the valley, with a superficial orifice, then the liquid will of course gush forth in a vertical column, and form a jet d’eau, or fountain, its height being determined by the elevation of the sheet of water by which it is fed, and the consequent degree of pressure which acts upon it. This is the principle on which all artificial fountains are constructed. The conduit, for instance, which feeds the grand fountain of the Tuileries receives its water from a reservoir situated on the heights of Chaillot.

Whatever the form of the tube may be in which the liquid is contained, the simple hydrostatic law which regulates its level remains unmodified. Let the tube be circular, elliptic, or square, with a single orifice or with many—let it be open or choked with pebbles or permeable sand—in every case the water will invariably rise to the same height, provided the tube be perfectly water-tight; or else gush forth wherever it finds an opening below the highest level.

This hydrostatic principle so perfectly illustrates the origin of springs, that it is almost superfluous to enter into any further details on the subject.

When we consider that porous or absorbent strata, alternating with impermeable strata, frequently crop out on the back or on the slope of hills or mountains, and then, having reached their base, extend horizontally beneath the plain, there can be no doubt that they are placed in the same hydrostatic conditions as ordinary water-conducting tubes, and that wherever any fissure or opening occurs in the superincumbent impervious strata at any point below the highest level of the water, springs must necessarily be formed.

As the same strata often extend over many hundreds of miles, we cannot wonder that sources frequently issue from the centre of immense plains, for the hydrostatic pressure which causes them to gush forth may have its seat at a very considerable distance.

As the waters by which the springs are fed have often vast subterranean journeys to perform, their temperature is naturally independent of that of the seasons or of the changes of the atmosphere. Thus, cold springs occur in a tropical climate, when their subterranean channels descend from high mountains, and boiling sources gush forth in the Arctic regions when forced upwards from a considerable depth.

While the waters filter through the earth, they also naturally dissolve a variety of substances, and hence all springs are more or less impregnated with extraneous particles. But many of them, particularly such as are of a higher temperature, contain either a larger quantity or so peculiar a combination of mineral substances as to acquire medicinal virtues of the highest order.

The geological phenomena which favour the production of thermal springs are extremely interesting, and point to a deep-seated origin. By far the greater number of these fountains arise near the scene of some great subterranean disturbance, either connected with volcanic action, or with the elevation of a chain of mountains, or lastly by cliffs and fissures caused by disruption. Thus the thermal springs of Matlock and Bath accompany great natural fissures in the mountain limestone, and the hot springs of Wiesbaden and Ems, of Carlsbad and Toeplitz, all lie contiguous to remarkable dislocations, or to great lines of elevation, or to the neighbourhood of a volcanic focus.

One of the most remarkable phenomena of thermal springs is the constant invariableness of their temperature and their mineral impregnation. During the last fifty or sixty years, ever since accurate thermometrical observations and chemical analyses have been made, the most celebrated mineral sources of Germany have been found to contain the same proportion of mineral substances. This is truly astonishing when we consider that the latter are merely dissolved by the waters while passing through the bowels of the earth, and that a considerable number of them are frequently found together in the same source.

Another remarkable fact is, that, even in countries exposed to violent and frequent earthquakes, so many subterranean watercourses have remained unaltered for 2,000 years at least. The sources of Greece still flow apparently as in the times of Hellenic antiquity. The spring of Erasinos, two leagues south of Argos, on the declivity of the Chaonian mountains, is mentioned by Herodotus. At Delphi the Cassotis (now Wells of Saint Nicholas) still flow under the ruins of the temple of Apollo, and the hot baths of Aidepsos still exist in which Sylla bathed during the Mithridatic war.

Many springs exhibit the singular phenomenon of an intermittence which is independent of the quantity of rain falling in the district, or of the flux and reflux of the tide in a neighbouring river. In many cases the simple and well-known hydrostatical law exemplified in the common siphon[^[3]] affords a very ready and sufficient explanation of the phenomenon.

In the annexed diagram the vessel a communicates, by a tube c, with the siphon tube b, and it is manifest that when the water in a rises above the level of the top of b, it will begin to flow over and escape, as at d. But as soon as this is the case the tube b begins to act as a siphon, and draws off all the water in a, so that if a constant supply is poured into a, but at a rate slower than the rate of the discharge at d, there will be an intermittent discharge, the interval depending on the relation of the rate of filling to that of emptying.

SECTION OF AN INTERMITTENT SPRING.

The case of a subterranean cavity in a limestone rock, slowly fed by drainage from the cracks and fissures of the rock above, and communicating at a distant point with the surface by a bent or siphon tube, is evidently strictly analogous.

GEYSIRS OF ICELAND.

Iceland, pre-eminently the land of volcanic wonders, possesses in the Great Geysir the most remarkable intermittent fountain in the world. ‘At the foot of the Laugarfjall hill, in a green plain, through which several rivers meander like threads of silver, and where chains of dark-coloured mountains, overtopped here and there by distant snow-peaks, form a grand but melancholy picture, dense volumes of steam indicate from afar the site of a whole system of thermal springs congregated on a small piece of ground not exceeding twelve acres in extent. In any other spot the smallest of these boiling fountains would arrest the traveller’s attention, but here his whole mind is absorbed by the Great Geysir. In the course of countless ages, this monarch of springs has formed out of the silica which it deposits a mound which rises to about thirty feet above the general surface of the plain, and slopes on all sides, to the distance of a hundred feet or thereabouts, from the border of a large circular basin situated in its centre, and measuring about fifty-six feet in the greatest diameter and fifty-two feet in the narrowest. In the middle of this basin, forming as it were a gigantic funnel, there is a pipe or tube, which at its opening in the basin is eighteen or sixteen feet in diameter, but narrows considerably at a little distance from the mouth, and then appears to be not more than ten or twelve feet in diameter. It has been probed to a depth of seventy feet, but it is more than probable that hidden channels ramify further into the bowels of the earth. The sides of the tube are smoothly polished, and so hard that it is not possible to strike off a piece of it with a hammer. Generally the whole basin is found filled up to the brim with sea-green water as pure as crystal, and of a temperature of from 180° to 190°. Astonished at the placid tranquillity of the pool, the traveller can hardly believe that he is really standing on the brink of the far-famed Geysir; but suddenly a subterranean thunder is heard, the ground trembles under his feet, the water in the basin begins to simmer, and large bubbles of steam rise from the tube and burst on reaching the surface, throwing up small jets of spray to the height of several feet. Every instant he expects to witness the grand spectacle which has chiefly induced him to visit this northern land; but soon the basin becomes tranquil as before, and the dense vapours produced by the ebullition are wafted away by the breeze. These smaller eruptions are regularly repeated every eighty or ninety minutes, but frequently the traveller is obliged to wait a whole day or even longer before he sees the whole power of the Geysir. A detonation louder than usual precedes one of these grand eruptions; the water in the basin is violently agitated; the tube boils vehemently; and suddenly a magnificent column of water, clothed in vapour of a dazzling whiteness, shoots up into the air with immense impetuosity, to the height of eighty or ninety feet, and, radiating at its apex, showers water and steam in every direction. A second eruption and a third rapidly follow, and after a few minutes the fairy spectacle has passed away like a fantastic vision. The basin is now completely dried up, and on looking down into the shaft, the traveller is astonished to see the water about six feet from the rim, and as tranquil as in an ordinary well. After about thirty or forty minutes it again begins to rise, and after a few hours reaches the brim of the basin. Soon the subterranean thunder, the shaking of the ground, the simmering above the tube begin again—a new gigantic explosion takes place, to be followed by a new period of rest—and thus this wonderful play of nature goes on, day after day, year after year, and century after century. The mound of the Geysir bears witness to its immense antiquity, as its water contains but a minute portion of silica.’[^[4]]

The explanation of these wonderful phenomena has exercised the ingenuity of many natural philosophers; but Professor Bunsen’s theory seems the most plausible. Having first ascertained, by experiment, that the water at the mouth of the tube has a temperature, corresponding to the pressure of the atmosphere, of about 212° F., he found it much hotter at a certain depth below; a thermometer, suspended by a string in the pipe, rising to 266° F., or no less than 48° above the boiling point. By letting down stones, suspended by strings, to various depths, he next came to the conclusion that the tube itself is the main seat or focus of the mechanical power which forces the huge water column upwards. For the stones which were sunk, to greater distances from the surface were not cast up again when the next eruption of the Geysir took place, whereas those nearer the mouth of the tube were ejected to a considerable height by the ascending water-column. Other experiments also were made, tending to demonstrate the singular fact that there is often scarcely any motion below when a violent rush of steam and water is taking place above. It seems that when a lofty column of water possesses a temperature increasing with the depth, any slight ebullition, or disturbance of equilibrium, in the upper portion may first force up water into the basin, and then cause it to flow over the edge. A lower portion, thus suddenly relieved of part of its pressure, expands, and is converted into vapour more rapidly than the first, owing to its greater heat. This allows the next subjacent stratum, which is much hotter, to rise and flash into a gaseous form; and this process goes on till the ebullition has descended from the middle to near the bottom of the funnel.[^[5]]

In many geological basins, the deep subterranean waters are frequently inclosed over a surface of many square miles between impermeable beds of clay or hard rock, which nowhere permit them to escape; but if a hole be bored deep enough to reach a permeable bed, it is evident that they will then gush forth more or less violently, according to the degree of hydrostatic pressure which acts upon them. This is the simple theory of the Artesian Wells, so called from the French province of Artois, where, as far back as the beginning of the twelfth century, springs of water were artificially obtained by perforating the soil to a certain depth in places where no indication of springs existed at the surface. The barbarous inhabitants of the Sahara seem, however, to have long preceded the Artesians in the art of sinking deep wells, for Olympiodorus, a writer who flourished at Alexandria about the middle of the sixth century, mentions pits sunk in the oasis to the depth of 200 or 300 yards, and pouring forth streams of water, used for irrigation.

By the aid of geological science, and of greater mechanical skill, Artesian borings[^[6]] are at present frequently undertaken in civilised countries, wherever the nature of the ground promises success, and the want of water is sufficiently great to warrant the attempt. Sometimes the water is reached at a moderate distance from the surface, but not seldom it has been found necessary to bore to a depth of 200 or 300 fathoms. Often efforts, even on this large scale, have proved vain, and the work has been abandoned in despair.

One of the most remarkable instances on record of a successful sinking for water is that of the Artesian well of Grenelle, one of the Parisian suburbs.

POROUS STRATA. ARTESIAN WELL SUNK IN THE LONDON BASIN.

The work was begun with an auger of about a foot in diameter, and the borings showed successively the alluvial soil and subsoil, and the tertiary sands, gravels, clays, lignite, &c., until the chalk was reached. The work was then carried on regularly through the hard upper chalk down to the lower chalk with green grains, the dimension of the auger being reduced at 500 feet to a nine-inch, and at 1,300 feet to a six-inch aperture. When the calculated depth of 1,500 feet had been reached, and as yet no result appeared, the Government began to be disheartened. Still, upon the urgent representations of the celebrated Arago, the sinking was continued, until at length, at the depth of 1,800 feet, the auger, after a violent shock which made the ground tremble, suddenly turned without an effort. ‘Either the auger is broken, or we have gained our end,’ exclaimed the director of the work; and a few moments after, a large column of water gushed out of the orifice. It took more than seven years to accomplish this grand work (1833–41), which was retarded by numberless difficulties and accidents. About half-a-million gallons of perfectly limpid water of a temperature of 82° Fahr. are daily supplied by the Puits de Grenelle, and amply repay its cost (362,432 fr. 65 centimes = 14,500l.).

The high temperature of Artesian springs, when rising from considerable depths, has been turned to various practical uses. Thus, near Canstadt, in Wurtemberg, several mills are kept in work, during the severest cold of winter, by means of the warm water of Artesian wells which has been turned into the mill-ponds, and at Heilbronn several proprietors save the expense of fuel by leading Artesian water in pipes through their green-houses. In some localities the pure and constantly temperate Artesian waters are made use of for the cultivation of cress. The vigorous growth of this salutary herb in the beds of rivulets, where natural springs gush forth, gave the idea of this application, which is so profitable that the cress nurseries of Erfurt yield a produce of 12,000l. a year. Fish ponds have also been improved by such warm springs being passed through them.

Among the localities benefited by the boring of Artesian wells, Venice deserves to be particularly noticed. Formerly the City of the Doges had no other supply of water but that which was conveyed by boats from the Brenta, or obtained from the rain collected in cisterns. Hence the joy of the inhabitants may be imagined, when, in 1846, an Artesian boring in the Piazza San Paolo began to disgorge its water at the rate of forty gallons per minute, and when other undertakings of the same kind proved equally successful.

Wherever a well gushes forth in the Sahara, it brings life into the wilderness; the date-tree flourishes as far as its fertilising waters extend, and the wandering Arab changes into a sedentary cultivator of the soil. Thus the boring of Artesian wells on the desert confines of South Algeria has been the means of wonderful improvement, and if the French have too often marked their dominion in Africa by a barbarous oppression of the Arabs, they, in this respect at least, appear in the more amiable light of public benefactors.

A boring apparatus was first landed at Philippeville in April 1856, and conveyed with immense difficulty to the Oasis Wad Rir at Tamerna. The work was begun in May, and on the 19th of June, a spring, to which the grateful inhabitants gave the name of the ‘Well of Peace,’ gushed forth. Soon after another source was tapped at Tamelhat, in the Oasis Temacen, and received the name of the ‘Well of God’s blessing.’

The beneficent instrument of abundance was now conveyed to the Oasis Sidi Rasched, fifteen miles beyond Tuggurt. Here the auger had scarcely reached a depth of 120 feet when a perfect stream gushed forth, which, according to the praiseworthy Arab custom, received the name of the ‘Well of Thanks.’ The opening of this wonderful source gave rise to many touching scenes. The Arabs came in throngs to witness the joyful spectacle: each of them poured some of the water over his head, and the mothers bathed their children in the gushing flood. An old scheik, unable to conceal his emotion, fell down upon his knees, and shedding tears of joy, fervently thanked God for having allowed him to witness such a day.

The next triumph was the boring of four wells in the desert of Morran, where previously no spring had existed. In the full expectation of success, everything had been prepared to turn this new source of wealth to immediate use, and part of a nomadic tribe instantly settled on the spot, and planted 1,200 date-trees. A dreary solitude was changed, as if by magic, into a scene of busy life.

These few examples suffice to show the vast services which Artesian wells are destined at some future time to render to many of the arid regions of Africa. Both in the Sahara and in the basin-shaped deserts, which extend, under various names, from the Cape Colony to the neighbourhood of Lake Ngami, there are, beyond all doubt, numberless spots where water, the fertilising element, may be extracted from the bowels of the earth.

In the droughty plains of Australia also a vast sphere of utility is reserved to the Artesian wells. Here, also, they will subdue the desert, unite one coast to another by creating stations in the wilderness, and, with every new source which they call to life, promote both material progress and intellectual improvement.

MIDDLE AND VALLEY LAKE CRATERS, MOUNT GAMBIER, SOUTH AUSTRALIA.

CHAPTER VI.
VOLCANOES.

Volcanic Mountains—Extinct and Active Craters—Their Size—Dangerous Crater-explorations—Dr. Judd in the Kilauea Pit—Extinct Craters—Their Beauty—The Crater of Mount Vultur in Apulia—Volcanoes still constantly forming—Jorullo and Isalco—Submarine Volcanoes—Sabrina and Graham’s Island—Santorin—Number of Volcanoes—Their Distribution—Volcanoes in a constant state of eruption—Stromboli—Fumaroles—The Lava Lakes in Kilauea—Volcanic Paroxysms—Column of Smoke and Ashes—Detonations—Explosion of Cones—Disastrous Effects of Showers of Ashes and Lapilli—Mud Streams—Fish disgorged from Volcanic Caverns—Eruption of Lava—Parasitic Cones—Phenomena attending the Flow of a Lava Stream—Baron Papalardo—Meeting of Lava and Water—Scoriæ—Lava and Ice—Vast Dimensions of several Lava Streams—Scenes of Desolation—Volcanoes considered as safety-valves—Probable Causes of Volcanoes.

Volcanoes are vents which either have communicated, or still communicate, by one or several chimney-like canals or shafts, with a focus of subterranean fire, emitting, or having once emitted, heated matter in a solid, semi-liquid, or gaseous state. The first eruption of a volcano necessarily leaves a mound of scoriæ and lava, while numerous eruptions at length raise mountains, which are frequently of an amazing extent and height. These mountains, which are generally called volcanoes, though in reality they are but an effect of volcanic action situated far beneath their base, are called extinct when for many centuries they have exhibited no signs of combustion—active, when, either perpetually or from time to time, eruptions or exhalations of lava, scoriæ, or gases take place from their summits, or from vents in their sides. Their shape is generally that of a more or less truncated cone; but while some, like Cotopaxi or the Peak of Teneriffe, rise with abrupt declivities in the shape of a sugar-loaf, others, like Mauna Loa in the island of Hawaii, gradually, and almost imperceptibly, ascend from a vast base embracing many miles in circuit.

Their heights also vary greatly. While some, like Madana in Santa Cruz, or Djebel Teir on the coast of the Red Sea, scarcely raise their summits a few hundred feet above the level of the ocean, others, like Chuquibamba (21,000 feet), or Aconcagua (22,434 feet), hold a conspicuous rank among mountains of the first class.

The summit of a volcano generally terminates in a central cavity or crater, where the eruptive channel finds its vent. Craters are sometimes regularly funnel-shaped, descending with slanting sides to the eruptive mouth, but more commonly they are surrounded with high precipitous rock-walls, while their bottom forms a plain, which is frequently completely horizontal, and sometimes of a considerable extent. Its surface is rough and uneven, from the mounds of volcanic sand, of scoriæ, or of hardened lava with which it is covered, and generally exhibits a scene of dreadful desolation, rendered still more impressive by the steam and smoke, which, as long as the volcano continues in an active state, issue from its crevices.

Within this plain, the eruptive orifice or mouth of the volcano is almost universally surrounded by an elevation, composed of ejected fragments of scoriæ thrown from the vent. Such cones are forming constantly at Vesuvius, one being no sooner destroyed by any great eruption, before another begins to take shape and is enlarged, till often it reaches a height of several hundred feet.

Thus the crater of an active volcano is the scene of perpetual change—of a continual construction and re-construction, and the sands of the sea do not afford a more striking image of inconstancy.

The various craters are of very different dimensions. While the chief crater of Stromboli has a diameter of only fifty feet, that of Gunong Tenger, in Java, measures four miles from end to end; and, though the depth of a crater rarely exceeds 1,000 or 1,500 feet, the spectator, standing on the brink of the great crater of Popocatepetl, looks down into a gulf of 8,000 feet.

From the colossal dimensions of the larger craters, it may well be imagined that their aspect exhibits some of the sublimest though most gloomy scenery in nature—the picture of old Chaos with all its horrors.

The volcano Gunong Tjerimai, in Java, which rises to the height of 9,000 feet, is covered with a dense vegetation up to the crater’s brink. On emerging from the thicket, the wanderer suddenly stands on the verge of an immense excavation encircled with naked rocks. He is obliged to hold himself by the branches of trees, or to stretch himself flat upon the ground, so as to be able to look down into the yawning gulf. The deep and inaccessible bottom of the crater loses itself in misty obscurity, and glimmers indistinctly through the vapours which are there slowly and incessantly ascending from its mysterious depths. All is desolate and silent, save when a solitary falcon, hovering over the vast chasm, awakes with her discordant screech the echoes of the precipice. Through a telescope may be seen, in various parts of the huge crater walls, swarms of small swallows, which have there built their nests, flying backwards and forwards. The eye can detect no other signs of life, the ear distinguish no other sound.

Humboldt describes the view down the crater of the Rucu-Pichincha—a volcano which towers above the town of Quito to a height of 15,000 feet—as the grandest he ever beheld during all his long wanderings. Guided by an Indian, he ascended the mountain in 1802, and after scaling, with great difficulty and no small danger, its steep and rocky sides, he at length looked down upon the black and dismal abyss, whence clouds of sulphurous vapour were rising as from the gates of hell.

The descent into the crater of an active volcano is at all times a difficult and hazardous enterprise, both from the steepness of its encircling rock walls, and the suffocating vapours rising from its bottom; but it is rare indeed that a traveller has either the temerity or the good fortune to penetrate as far as the very mouth of the eruptive channel, and to gain a glimpse of its mysterious horrors. When M. Houel visited Mount Etna in 1769, he ventured to scale the cone of stones and ashes which had been thrown up in the centre of the crater, where thirty years before there was only a prodigious chasm or gulf. On ascending this mound, which emitted smoke from every pore, the adventurous traveller sunk about mid-leg at every step, and was in constant terror of being swallowed up. At last, when the summit was reached, the looseness of the soil obliged him to throw himself down flat upon the ground, that so he might be in less danger of sinking, while at the same time the sulphurous exhalations arising from the funnel-shaped cavity threatened suffocation, and so irritated his lungs as to produce a very troublesome and incessant cough. In this posture the traveller viewed the wide unfathomable gulf in the middle of the crater, but could discover nothing except a cloud of smoke, which issued from a number of small apertures scattered all around. From time to time dreadful sounds issued from the bowels of the volcano, as if the roar of artillery were rebellowed throughout all the hollows of the mountain. They were no doubt occasioned by the explosions of pent-up gases striking against the sides of these immense caverns, and multiplied by their echoes in an extraordinary manner. After the first unavoidable impression of terror had been overcome, nothing could be more sublime than these awful sounds, which seemed like a warning of Etna not to pry too deeply into his secrets.

Dr. Judd, an American naturalist, who, in 1841, descended into the crater of Kilauea, on Mauna Loa, in Hawaii, well-nigh fell a victim to his curiosity. At that time, the smallest of the two lava pools which boil at the bottom of that extraordinary pit appeared almost inactive, giving out only vapours, with an occasional jet of lava at its centre. Dr. Judd, considering the quiet favourable for dipping up some of the liquid with an iron ladle, descended for the purpose to a narrow ledge bordering the pool. While he was preparing to carry out his plans, his attention was excited by a sudden sinking of its surface; the next instant it began to rise, and then followed an explosion, throwing the lava higher than his head. He had scarcely escaped from his dangerous situation, the moment after, by the aid of a native, before the lava boiled up, covered the place where he stood, and, flowing out over the northern side, extended in a stream a mile wide to a distance of more than a mile and a half!

In extinct volcanoes, the picture of desolation originally shown by their craters has not seldom been changed into one of charming loveliness. Tall forest trees cover the bottom of the Tofua crater in Upolu, one of the Samoan group; and in the same island, a circular lake of crystal purity, belted with a girdle of the richest green, has formed in the depth of the Lanuto crater.

EXTINCT CRATER OF HALEAKALA.

The lakes of Averno near Naples, and of Bolsena, Bracciano, and Ronciglione, likewise fill the hollows of extinct craters, constituting scenes of surpassing beauty, rendered still more impressive by the remembrance of the stormy past which preceded their present epoch of tranquillity and peace. Mr. Mallet describes, with glowing colours, the singular beauty of

the forest scenery around the two extinct craters of Mount Vultur in Apulia, which time has converted into two deep circular lakes.

‘I descend amongst aged trunks and overarching limbs, and pass over masses of rounded lava-blocks and cemented lapilli. All is quietude; the soft breeze of a quiet winter’s afternoon fans across the embosomed water, from the early wheat-fields and the furrowed acres of the opposite steep slopes, and brings the gentle ripple lapping amongst the roots of the old hazels at my feet.

‘Off before me, and to my left, crowning the slope, are the grey ruins of some ancient church or castle, and far above me to the right, nestled against the lava crags, behind and above it, standing out white and clear, I see the strong buttressed mass of the monastery of St. Michael. How hard it is to realise that this noble and lovely scene, full of every leafy beauty, was once the innermost bowl of a volcano; that every stone around me, now glorious in colour with moss and lichen, sedum and geranium, was once a glowing mass, vomited from out that fiery and undiscovered abyss, which these placid waters now bury in their secret chambers.’

The line of demarcation between active and extinct volcanoes is not easily drawn, as eruptions have sometimes taken place after such long intervals of repose as to warrant the belief that the vents from which they issued had long since been completely obliterated. Thus, though nearly six centuries have passed since the last eruption of Epomeo in the island of Ischia, we are not entitled to suppose it extinct, since nearly seventeen centuries elapsed between this last explosion and the one which preceded it. Since the beginning of the fourteenth century Vesuvius also enjoyed a long rest of nearly three hundred years. During this time the crater got covered with grass and shrubs, oak and chestnut trees grew around it, and some warm pools of water alone reminded the visitor of the former condition of the mountain, when, suddenly, in December 1631, it resumed its ancient activity, and seven streams of lava at once burst forth from its subterranean furnaces.

While, in many volcanic districts, such as that of the Eifel on the left bank of the Rhine, and of Auvergne, in Central France, the once active subterranean fires have long since been extinguished, and no eruption of lava has been recorded during the whole period of the historic ages, new volcanoes, situated at a considerable distance from all previously active vents, have arisen from the bowels of the earth, almost within the memory of living man. From the era of the discovery of the New World to the middle of the last century, the country between the mountains Toluca and Colima, in Mexico, had remained undisturbed, and the space, now the site of Jorullo, which is one hundred miles distant from each of the above-mentioned volcanoes, was occupied by fertile fields of sugarcane and indigo, and watered by two brooks. In the month of June 1759, hollow sounds of an alarming nature were heard, and earthquakes succeeded each other for two months, until, at the end of September, flames issued from the ground, and fragments of burning rocks were thrown to prodigious heights. Six volcanic cones, composed of scoriæ and fragmentary lava, were formed on the line of a chasm, which ran in the direction of N.E. to S.W. The least of the cones was 300 feet in height, and Jorullo, the central volcano, was elevated 1,600 feet above the level of the plain. The ground where now, in Central America, Isalco towers in proud eminence, was formerly the seat of an estancia or cattle-estate. Towards the end of the year 1769, the inhabitants were frequently disturbed by subterranean rumblings and shocks, which constantly increased in violence, until on February 23, 1770, the earth opened, and pouring out quantities of lava, ashes, and cinders gave birth to a new volcanic mountain.

Besides those volcanic vents which are situated on the dry land, there are others which, hidden beneath the surface of the sea, reveal their existence by subaqueous eruptions. Columns of fire and smoke are seen to rise from the discoloured and agitated waters, and sometimes new islands are gradually piled up by the masses of scoriæ and ashes ejected from the mouth of the submarine volcano. In this manner the island of Sabrina rose from the bottom of the sea, near St. Michael’s in the Azores, in the year 1811; and still more recently, in 1831, Graham’s Island was formed in the Mediterranean, between the coast of Sicily and that projecting part of the African coast where ancient Carthage stood. Slight earthquake shocks preceded its appearance, then a column of water like a water-spout, 60 feet high and 800 yards in circumference, rose from the sea, and soon afterwards dense volumes of steam, which ascended to the height of 1,800 feet. Then a small island, a few feet high with a crater in its centre, ejecting volcanic matter, and immense columns of vapour, emerged from the agitated waters, and in a fortnight swelled to the ample proportions of a height of 200 feet, and a circumference of three miles. But both Sabrina and Graham’s Island, being built of loose scoriæ, were soon corroded by the waves, and their last traces have long since disappeared under the surface of the ocean.

Near Pondicherry, in India; near Iceland, in the Atlantic Ocean; half a degree to the south of the equator in the prolongation of a line drawn from St. Helena to Ascension; near Juan Fernandez, &c., similar phenomena have occurred within the last hundred years, but, probably, nowhere on a grander scale than in the Aleutian Archipelago, where, about thirty miles to the north of Unalaska, near the isle of Umnack, a new island, now several thousand feet high and two or three miles in circumference, was formed in 1796. The whole bottom of the sea between this new creation of the volcanic powers and Umnack has been raised by the eruptive throes which gave it birth; and where Cook freely sailed in 1778, numberless cliffs and reefs now obstruct the passage of the mariner.

The famous subaqueous volcano which, in the year 186 before the Christian era, began its series of historically recorded eruptions, by raising the islet of Hiera (the ‘Sacred’) in the centre of the Bay of Santorin, opened two new vents in 1866. Amid a tremendous roar of steam and the shooting up of prodigious masses of rock and ashes, two islets were formed, which ultimately rose to the height of 60 and 200 feet. The eruption continued for many months, to the delight and wonder of the numerous geologists who came from all sides to witness the extraordinary spectacle. Thus, in many parts of the ocean, we see the submarine volcanic fires laying the foundations of new islands and archipelagos, which, after repeated eruptions following each other in the course of ages, will probably, like Iceland, extend over a considerable space and become the seats of civilised man.

Map of the World
Showing the Distribution of
VOLCANOES
& the Districts visited by
EARTHQUAKES
.li
[Larger view]
.li-

As a very considerable part of the globe has never yet been scientifically explored, it is, of course, impossible to determine the exact number of the extinct and active volcanoes which are scattered over its surface. Werner gives a list of 193 volcanoes, and Humboldt mentions 407, of which 225 are still in a state of activity. The newest computation of Dr. Fuchs, of Heidelberg,[^[7]] increases the number to a total of 672, of which 270 are active. Future geographical discoveries will, no doubt, make further additions to the list, and show that at least through a thousand different vents the subterranean fires have, at various periods of the earth’s history, piled up their cones of scoriæ and lava.

The volcanoes are very unequally distributed over the surface of the globe, for, while in some parts they are thickly clustered together in groups or rows, we find in other parts vast areas of land without the least sign of volcanic action.

An almost uninterrupted range of volcanoes extends in a sinuous line from the Gulf of Bengal, through the East Indian Archipelago, the Moluccas, the Philippines, Formosa, Japan, and the Kuriles, to Kamtschatka. This desolate peninsula is particularly remarkable for the energy of its subterranean fires, as Ermann mentions no less than twenty-one active volcanoes, ranged in two parallel lines throughout its whole length, and separated from each other by a central range of mountains, containing a large and unknown number of extinct craters.

In Java, where more than thirty volcanoes are more or less active, the furnaces of the subterranean world are still more concentrated and dreadful.

The immense mountain-chains which run parallel to the western coasts of America are likewise crowned with numerous volcanic peaks. Chili alone has fourteen active volcanoes, Bolivia and Peru three, Quito eleven. In Central America we find twenty-one volcanoes, which are chiefly grouped near the Lake of Nicaragua, and to the west of the town of Guatemala.

The peninsula of Aljaska, and the chain of the Aleütes, possess no less than thirty-six volcanos, scattered over a line about 700 miles long; and thus we find the eastern, western, and northern boundaries of the Pacific encircled with a girdle of volcanic vents, while the subterranean fires have left the western shores of the Atlantic comparatively undisturbed.

With the exception of Iceland, which is famous for the widely devastating eruptions of its burning mountains, the volcanic energies of Europe are at present limited to the submarine crater of Santorin, and to the small area of Etna, Vesuvius, and the Lipari Islands. But, situated in the centre of the ancient seats of civilisation, and for so many centuries the object of the naturalist’s researches, of the traveller’s curiosity, and of the poet’s song, they surpass in renown all other volcanic regions in the world. Most other volcanoes vent their fury over lands either so wild or so remote that the history of their eruptions almost sounds like a legend from another planet; but thousands of us have visited Etna and Vesuvius, and the explosion of their rage menaces towns and countries which classical remembrances have almost invested with the interest of home.

Some volcanoes are in a continual state of eruption. Isalco, born, as we have seen, in 1770, has remained ever since so active as to deserve the name of the Faro (lighthouse) of San Salvador. Its explosions occur regularly, at intervals of from ten to twenty minutes, and throw up a dense smoke and clouds of ashes and stones. These, as they fall, add to the height and bulk of the cone, which is now about 2,500 feet high. For more than two thousand years, the fires of Stromboli have never been extinct, nor has it ever failed to be a beacon to the mariner while sailing after nightfall through the Tyrrhenian Sea. Mr. Poulett Scrope, who visited Stromboli in 1820, and looked down from the edge of the crater into the mouth of the volcano, some 300 feet beneath him, found the phenomena precisely such as Spallanzani described them in 1788. ‘Two rude openings show themselves among the black chaotic rocks of scoriform lava which form the floor of the crater. One, is to appearance, empty, but from it there proceeds, at intervals of a few minutes, a rush of vapour, with a roaring sound, like that of a smelting furnace when the door is opened, but infinitely louder. It lasts about a minute. Within the other aperture, which is perhaps twenty feet in diameter, and but a few yards distant, may be distinctly perceived a body of molten matter, having a vivid glow even by day, approaching to that of white heat, which rises and falls at intervals of from ten to fifteen minutes. Each time that it reaches in its rise the lip of the orifice, it opens at the centre, like a great bubble bursting, and discharges upwards an explosive volume of dense vapour, with a shower of fragments of incandescent lava and ragged scoriæ, which rise to a height of several hundred feet above the lip of the crater.’

The volcanoes of Masaya, near the lake of the same name in Nicaragua; of Sioa, in the Moluccas; and of Tofua, in the Friendly Islands, are also, like Stromboli, in a state of permanent eruption. But far more commonly the volcanoes burst forth only from time to time in violent paroxysms, separated from each other by longer phases of moderate activity, during which their phenomena are confined to the exhalation of vapours and gases, sometimes also to the ejection of scoriæ or ashes; to the oscillations of lava rising or subsiding in the shaft of the crater, to the gentle outflow of small streams of lava from its eruptive cone, and to slight commotions of its border. A continual or periodical exhalation of steam and gases from the shaft of the crater or from chasms and fissures in its bottom, is the commonest phenomenon shown by an active volcano while in a state of tranquillity. Aqueous vapours compose the chief part of these exhalations, and along with other volatile substances, such as sulphuretted hydrogen, sulphurous acid, muriatic acid, and carbonic acid, form the steam-jets or fumaroles, which escape with a hissing or roaring noise from all the crevices and chasms of the crater, and, uniting as they ascend in a single vapour-cloud, ultimately compose the lofty column of steam which forms so conspicuous a feature in the picturesque beauty of Etna or Vesuvius. High on the summit of Mauna Loa, where all vegetation has long since ceased, the warm steam of the fumaroles gives rise to a splendid growth of ferns in crevices sheltered from the wind; and on the island of Pantellaria, the shepherds, by laying brushwood before the fumaroles, condense the steam, and thus procure a supply of water for their goats.

The gentle fluctuations of lava in a crater while in a state of moderate activity are nowhere exhibited on a grander scale than in the pit of Kilauea on Mauna Loa. The mountain rises so gradually as almost to resemble a plain, and the crater appears like a vast gulf excavated in its flanks. The traveller perceives his approach to it by a few small clouds of steam, rising from fissures not far from his path. While gazing for a second indication, he stands unexpectedly upon the brink of the pit. A vast amphitheatre seven miles and a half in circuit has opened to view. Beneath a gray rocky precipice of 650 feet, a narrow plain of hardened lava extends, like a vast gallery, around the whole interior. Within this gallery, below another similar precipice of 340 feet, lies the bottom, a wide plain of bare rock more than two miles in length. Here all is black monotonous desolation, excepting certain spots of a blood-red colour, which appear to be in constant yet gentle agitation.

When Professor Dana visited Kilauea (December 1840), he was surprised at the stillness of the scene. The incessant motion in the blood-red pools was like that of a cauldron in constant ebullition. The lava in each boiled with such activity as to cause a rapid play of jets over its surface. One pool, the largest of the three then in action, was afterwards ascertained by survey to measure 1,500 feet in one diameter and 1,000 in another; and this whole area was boiling, as seemed from above, with nearly the mobility of water. Still all went on quietly. Not a whisper was heard from the fires below. White vapours rose in fleecy wreaths from the pools and numerous fissures, and above the large lake they collected into a broad canopy of clouds, not unlike the snowy heaps or cumuli that lie near the horizon on a clear day, though their fanciful shapes changed more rapidly.

On descending afterwards to the black ledge or gallery at the verge of the lower pit, a half-smothered gurgling sound was all that could be heard from the pools of lava. Occasionally, there was a report like that of musketry, which died away, and left the same murmuring sound, the stifled mutterings of a boiling fluid.

Such was the scene by day—awful, melancholy, dismal—but at night it assumed a character of indescribable sublimity. The large cauldron, in place of its bloody glare, now glowed with intense brilliancy, and the surface sparkled with shifting points of dazzling light, occasioned by the jets in constant play. The broad canopy of clouds above the pit, which seemed to rest on a column of wreaths and curling heaps of lighted vapour, and the amphitheatre of rocks around the lower depths, were brightly illuminated from the boiling lavas, while a lurid red tinged the distant parts of the inclosing walls and threw their cavernous recesses into deeper shades of darkness. Over this scene of restless fires and fiery vapours, the heavens by contrast seemed unnaturally black, with only here and there a star, like a dim point of light.

A paroxysmal eruption is generally announced by the intensification of the phenomena above described. Slight earthquakes are felt in the neighbourhood of the volcano, and follow each other in more rapid succession and with greater violence as the catastrophe draws near. A deep noise like the rolling of thunder, or like the roar of distant artillery, is heard under the ground; the white steam from the crater ascends in denser clouds, which soon acquire a darker tinge; and now the bottom of the crater suddenly bursts with a terrific crash, and with the rapidity of lightning, an immense column of black smoke shoots up into the air, and, expanding at its upper end into a broad horizontal canopy, assumes a shape which has been compared with that of the Italian pine, the graceful tree of the South. As the column of smoke spreads over the sky, it obscures the light of the sun and changes day into night. Along with the smoke, showers of glowing lava are cast high up into the air, and, rising like rockets, either fall back into the crater or rattle down the declivity of the cone.

At night the scene assumes a character of matchless grandeur, when the column of smoke—or, more properly speaking, of scoriæ, vapour, and impalpable dust—is illuminated by the vivid light of the lava glowing in the crater beneath. It then appears as an immense pillar of fire, rising with steady majesty in the midst of the uproar of all the elements, and ever and anon traversed by flashes of still greater brilliancy from the masses of liquid lava hurled forth by the volcano.

The detonations which accompany an eruption are sometimes heard as single crashes, at others as a rolling thunder or as a continuous roaring. They are frequently audible at an astonishing distance, over areas of many thousand square miles, and with such violence that they may be supposed to proceed from the immediate neighbourhood. Thus, during the eruption of Cosiguina in Nicaragua, which took place in the year 1834, the detonations were heard as loud as a thunderstorm in the neighbourhood of Kingston in Jamaica, and even at Santa Fé de Bogota, which is a thousand miles distant from the volcano. With the increase of steam generated during an eruption, the quantity of ejected scoriæ likewise increases in an astonishing manner, so that the volcano’s mouth resembles a constantly discharging mine of the most gigantic dimensions.

The stones and ashes projected during a volcanic eruption vary considerably in size, from blocks twelve or fifteen feet in diameter to the finest dust. Both their immense quantity, and the force with which they are hurled into the air, show the utter insignificance of the strength displayed by the most formidable engines invented by man when compared with elementary power. Huge blocks are shot forth, as from the cannon’s mouth, to a perpendicular elevation of 6,000 feet, and La Condamine relates that in 1533 Cotopaxi hurled stones of eight feet in diameter in an oblique direction to the distance of seven miles. The lighter scoriæ, carried far away by the winds, not seldom bury whole provinces under a deluge of sand and ashes; and their disastrous effects, spreading over an immense area, are frequently greater than those of the lava-streams, whose destructive power is necessarily confined to a narrower space. To cite but a few examples, the rain of sand and ashes which in 1812 menaced the Island of St. Vincent with the fate of Pompeii soon buried every trace of vegetation, and the affrighted planters and negroes fled to the town. But here also the black sand, along with many larger stones, fell rattling like hail upon the roofs of the houses, while at the same time a tremendous subterranean thunder increased the horrors of the scene. Even Barbadoes, though eighty miles from St. Vincent’s, was covered with ashes. A black cloud, approaching from the sea, brought with it such pitchy darkness that in the rooms it was impossible to distinguish the windows, and a white pocket-handkerchief could not be seen at a distance of five inches.

The fall of ashes caused in April 1815 by the eruption of the Temboro, in Sumbawa, not only devastated the greater part of the island, but extended in a westerly direction to Java, and to the north, as far as Celebes, with such an intensity that it became perfectly dark at noon. The roofs of houses at the distance of forty miles were broken in by the weight of the ashes that fell upon them. To the west of Sumatra the surface of the sea was covered two feet deep with a layer of floating pumice or scoriæ, through which ships with difficulty forced their way.

By the terrific eruption of Cosiguina in the Gulf of Fonseca, in Central America, in 1835, all the ground within a radius of twenty-five miles was loaded with scoriæ and ashes to the depth of ten feet and upwards, while the lightest and finest ash was carried by the winds to places more than 700 miles distant. Eight leagues to the southward of the crater the ashes covered the ground to the depth of three yards and a half, destroying the woods and dwellings. Thousands of cattle perished, their bodies being in many instances one mass of scorched flesh. Deer and other wild animals sought the towns for protection; birds and beasts were found suffocated in the ashes, and the neighbouring streams were strewed with dead fish.

When we consider the amazing quantity of stones and ashes ejected in these and similar instances by volcanic power, we cannot wonder that considerable mountains have frequently been piled up by one single eruption. Thus in the Bay of Baiæ near Naples, Monte Nuovo, a hill 440 feet high, and with a base of more than a mile and a half in circumference, formed, in less than twelve hours, on September 29, 1538; and a few days gave birth to Monte Minardo, near Bronte, on the slopes of Etna, which rises to the still more considerable height of 700 feet. It would be curious to calculate how many thousands of workmen, and what length of time, man would need to raise mounds like these, produced by an almost instantaneous effort of nature.

In other cases the expansive power of the elastic vapours, which cast up these prodigious masses from the bowels of the earth, is such as to blow to pieces the volcanic cone through which it seeks its vent.

In Quito there is an ancient tradition that Capac Urcu, which means ‘the chief,’ was once the highest volcano near the equator, being higher than Chimborazo, but at the beginning of the fifteenth century a prodigious eruption took place which broke it down. The fragments of trachyte, says Mr. Boussingault, which once formed the conical summit of this celebrated mountain, are at this day spread over the plain. On August 11, 1772, the Pepandajan, in Java, formerly one of the highest mountains of the island, broke out in eruption; the inhabitants of the country around prepared for flight, but, before they could escape, the greater part of its summit was shivered to pieces and covered the neighbourhood with its ruins, so that in the upper part of the Gurat valley forty villages were completely buried. During the dreadful eruption of 1815, the Temboro, in Sumbawa, is said to have lost at least one-third of its height from the explosion of its summit, and similar instances are mentioned as having occurred among the volcanoes of Japan.

In the year 1638 a colossal cone called the Peak, in the Isle of Timor, one of the Moluccas, was entirely destroyed by a paroxysmal explosion. The whole mountain, which was before this continually active, and so high that its light was visible, it is said, three hundred miles off, was blown up and replaced by a concavity now containing a lake.

Again, according to M. Moreau de Jonnes, in 1718, on March 6–7, at St. Vincent’s, one of the Leeward Isles, the shock of a terrific earthquake was felt, and clouds of ashes were driven into the air, with violent detonations, from a mountain situated at the eastern end of the island. When the eruption had ceased, it was found that the whole mountain had disappeared like the baseless fabric of a dream.

The disastrous effects of the showers of sand, pumice, and lapilli ejected by a volcanic eruption are increased by the transporting power of water. The aqueous vapours which are evolved so copiously from volcanic craters during eruptions, and often for a long time subsequently to the discharge of scoriæ and lava, are condensed as they ascend in the cold atmosphere surrounding the high volcanic peak; and the clouds thus formed, being in a state of high electrical tension, give rise to terrific thunderstorms. The lightning flashes in all directions from the black canopy overhanging the mountain, the perpetually rolling thunder adds its loud voice to the dreadful roar of the labouring volcano, while torrents of rain, sweeping along the light dust and scoriæ which they carry down with them from the air, or meet with on their way, produce currents of mud, often more dreaded than streams of lava, from the far greater velocity with which they move.

It not seldom happens that the eruptions of volcanoes rising above the limits of perpetual snow are preceded or accompanied by the rapid dissolution of the ice which clothes their summits or their sides, owing to the high temperature imparted to the whole mass of the mountain by the vast conflict raging within. Thus in January 1803 one single night sufficed to dissolve or sweep away the enormous bed of snow which in times of rest covers the steep cone of Cotopaxi (18,858 feet high), so that on the following morning the dark mountain, divested of its brilliant robe, gave warning to the affrighted neighbourhood of the terrific scenes that were about to follow. The volcanoes of Iceland, which mostly rise in the midst of vast fields of perpetual ice, frequently exhibit this phenomenon. On October 17, 1758, the eruptive labouring of Kötlingia gave birth to three enormous torrents, which carried along with them such masses of glacier fragments, sand, and stones as to cover a space fifty miles long and twenty-five miles broad. Blocks of ice as large as houses, and partly bearing immense pieces of stone on their backs, were hurried along by the floods; and soon after the eruption took place with a terrific noise.

A very singular phenomenon sometimes occurs in the gigantic volcanoes of the Andes. By the infiltration of water into the crevices of the trachytic rock of which they are composed, the caverns situated at their declivities or at their foot are gradually changed into subterranean lakes or ponds, which frequently communicate by narrow apertures with the Alpine brooks of the highlands of Quito. The fish from these brooks live and multiply in these subterranean reservoirs thus formed, and when the earthquakes which precede every eruption of the Andes chain shake the whole mass of the volcano, the caverns suddenly open and discharge enormous quantities of water, mud, and small fish.

When in the night between the 19th and 20th of June 1698, the summit of Carguairazo (18,000 feet high) was blown up, so that of the whole crater-rim but two enormous peaks remained, the inundated fields were covered, over a surface of nearly fifty square miles, with fluid tuff and clay-mud enveloping thousands of dead fish. Seven years before, the malignant fever which prevailed in the mountain-town of Ibarra to the north of Quito was attributed to the effluvia arising from the putrid fish ejected by the volcano of Imbaburu.

Amidst all these terrible phenomena—the dreadful noise, the quaking of the earth, the ejection of stones and ashes—which, often continuing for weeks or months, shake the deepest foundations of the volcano, fiery streams of liquid lava gush forth sooner or later as from a vase that is boiling over. Their appearance generally indicates the crisis of the subterranean revolution, for the rage of the elements, which until then had been constantly increasing, diminishes as soon as the torrent has found an outlet. The lava rarely issues from the summit crater of the mountain; much more frequently it flows from a lateral rent in the volcano’s side, which, weakened and dislocated in its texture by repeated shocks, at length gives way to the immense pressure of the lava column boiling within. From the vast size of these eruptive rents, we may form some idea of the gigantic power of the forces which give them birth.

Thus during the great eruption of Etna in 1669, the south-east flank of the mountain was split open by an enormous rent twelve miles long, at the bottom of which incandescent lava was seen. The extreme length of the fissure which gave lateral issue to the lava of Kilauea in 1840 was twenty-five miles, as could distinctly be traced through the disturbance of the surface rocks above; and in the terrific eruption of Skaptar Jökul, which devastated the west coast of Iceland in 1783, lava gushed forth from several vents along a fissure of not less than 100 miles in length. In some cases the whole mass of the volcano has been cleft in two. Vesuvius was thus rent in October 1822 by an enormous fissure broken across its cone in a direction N.W.—S.E.

Here and there along the line of such a rent, cones of eruption are thrown up in succession at points where the gaseous matter obtains the freest access to the surface, and has power to force up lava and scoriæ. Few indeed, if any, of the greater volcanic mountains are unattended by such minor elevations, clustering about its sides like the satellites of a planet. Professor Dana found Mauna Loa covered with numerous parasitic cones, and Mr. Darwin counted several thousands on one of the Gallapagos Islands. On the flanks of Etna, according to Professor Sartorius von Waltershausen, more than 700 of them are to be seen, almost all possessing craters, and each marking the source of a current of lava. Though they appear but trifling irregularities when viewed from a distance as subordinate parts of so imposing and colossal a mountain, many of them would nevertheless be deemed hills of considerable height in almost any other region. The double hill near Nicolosi, called Monte Rossi, formed in 1669, is 450 feet high and two miles in circumference at its base; and Monte Minardo, near Bronte, on the east of the great volcano, is upwards of 700 feet in height.[^[8]]

‘On looking down from the lower borders of the desert region of Etna,’ says Sir Charles Lyell, ‘these minor volcanoes, which are most abundant in the woody region, present us with one of the most delightful and characteristic scenes in Europe. They afford every variety of height and size, and are arranged in beautiful and picturesque groups. However uniform they may appear when seen from the sea, or the plains below, nothing can be more diversified than their shape when we look from above into their craters, one side of which, as we have seen, is generally broken down. There are indeed, few objects in nature more picturesque than a wooded volcanic crater. The cones situated in the higher parts of the forest zone are chiefly clothed with lofty pines, while those at a lower elevation are adorned with chestnuts, oaks, and beech-trees.’

As the point where a lava-current finds a vent is often situated at a considerable distance below the surface of the liquid column in the internal chimney of the volcano, the pressure from above not seldom causes the lava to spout forth in a jet, until its level in the crater shaft has been reduced to that of the newly-formed orifice. Thus, when Vesuvius was rent by the dreadful paroxysmal eruption of 1794, the lava was seen to shoot up in magnificent fountains as it issued from the openings along the fissure.

Further on, the lava flows down the mountain’s side according to the same laws which regulate the movements of any other stream, whether of water, mud, or ice: more rapidly down an abrupt declivity, slower where the slope is more gradual; now accumulating in narrow ravines, then spreading out in plains; sometimes rushing in fiery cascades down precipices, and, where insurmountable obstacles oppose its progress, not seldom breaking off into several branches, each of which pursues its independent course.

At the point where it issues, the lava flows in perfect solution, but, as its surface rapidly cools when exposed to the air, it soon gets covered with scoriæ, which are dashed over each other in wild confusion, by successive floods of liquid stone, so as to resemble a stormy sea covered with ice-blocks. But the liquefied stone not only hardens on its external surface; it also becomes solid below, where it touches the colder soil, so that the fluid lava literally moves along in a crust of scoriæ, which lengthens in the same proportion as the stream advances.

The movements of the lava-current are of course considerably retarded by the formation of scoriæ, so that, unless where a greater inclination of the soil gives it a new impulse, it flows slower and slower. Thus the lava-stream which was ejected by Etna during the great eruption of 1669, performed the first thirteen Italian miles of its course in twenty days, or at the average rate of 162 feet per hour, but required no less than twenty-three days for the last two miles. While moving on, its surface was in general a mass of solid rock; and its mode of advancing, as is usual with lava streams, was by the occasional fissuring of the solid walls. Yet, in spite of the tardiness of its progress, the inhabitants of Catania watched its advance with dismay, and rushed into the churches to invoke the aid of the Madonna and the Saints. One citizen only, a certain Baron Papalardo, relied more upon his own efforts than upon supernatural assistance, and set out with a party of fifty men, dressed in skins to protect them from the heat, and armed with iron crows and hooks for the purpose of breaking open one of the solid walls of scoriæ that flanked the liquid current, so as to divert it from the menaced city. A passage was thus opened for a rivulet of melted matter, which flowed in the direction of Paterno; but the inhabitants of that town being alarmed for their safety, took up arms against Papalardo, whose fifty workmen would hardly have been able to cope with the powers of nature. Thus, slowly but irresistibly, the lava advanced up to the walls of Catania, which, being formed of huge Cyclopean blocks, and no less than sixty feet high, at first stemmed the fiery stream. But the glowing floods, pressing against the rampart, rose higher and higher, and finally reaching its summit, rushed over it in fiery cataracts, and destroying part of the town, at length disgorged themselves into the sea, where they formed a not inconsiderable promontory.

A truly gigantic conflict might naturally be expected from the meeting of two such powerful and hostile bodies as fire and water. This, however, is by no means the case, for as soon as the lava enters the sea, the rapid evaporation of the water that comes into immediate contact with it accelerates the cooling of the surface and thickens the hard external crust to such a degree that very soon all communication is cut off between the water and the fiery mass. While the lava continues to advance from the land, the crust of scoriæ is prolonged in the same proportion, and should it be rent here and there, steam is at once developed with such violence as to prevent all further access of the water into the interior of the fissures. Thus, Breislak informs us that, in 1794, the eruption of a lava-stream into the Bay of Naples, near Torre del Greco, took place with the greatest tranquillity, so that he himself was able to observe the advancing of the lava into the sea while seated in a boat immediately near it, without being disturbed by explosions or any other violent phenomenon.

As the crust of scoriæ is so bad a conductor of heat, it occasions a very slow cooling and hardening in the interior of the lava-stream, forming as it were a vessel in which the liquid fire can be retained and preserved for a long time. When Elie de Beaumont visited the lava-stream of Etna, nearly two years after its eruption in 1832, its interior was still so warm that he could not hold his finger in the hot steam issuing from its crevices. It has also been proved, on trustworthy evidence, that after twenty-five and thirty years, many lava-streams of Etna still continued to emit heat and steam; and after twenty-one years it was possible to light a cigar in the crevices of the lava that issued from Jorullo in 1759.

Another extremely curious effect of the scoriæ being such bad conductors of heat is, that masses of snow will remain unmelted, though a lava-stream rolls over them. Thus, in 1787, the lava of Etna flowed over a large deposit of snow, which, however, was by no means fully liquefied, but remained for the greatest part entire, and gradually changed into a granular and solid mass of ice. This was traced in 1828, by the geologist Gemellaro, for a distance of several hundred feet under the lava, and most likely still reposes under it as in an ice-cellar. The cliffs which form the vast crater-ring of the Isle of Deception, in the extreme Southern Atlantic, are likewise composed of alternate layers of ice and lava. Probably in both these cases the ice-beds had been covered before the lava flowed over them, by a rain of scoriæ and volcanic sand, which is so well known among the shepherds in the higher regions of Etna as a bad conductor of caloric, that, to obtain a supply of water for their herds during the summer, they cover some snow a few inches deep with volcanic sand, which entirely prevents the penetration of solar heat.

Most of the recent lava-streams evolve from all their fissures and rents a quantity of vapour, so as to be dotted with innumerable fumaroles, and to exhibit, as they flow along, a smoking surface by day and a luminous one by night. At first these fumaroles are so impetuous that they frequently puff up the lava-crust around their orifices into little cones or hillocks, consisting of blocks of scoriæ irregularly piled up over each other, and from whose summit the vapours continue to ascend. As the mass cools, they are naturally lessened in numbers and in power; but in 1803 Humboldt still saw fumaroles from twenty to thirty feet high, rising from the small cones which covered by thousands the great lava-stream of Jorullo of the year 1759.

The vast dimensions of single lava-streams give proof of the enormous powers which forced them out of the bowels of the earth. The lava-stream of Vesuvius which destroyed Torre del Greco in 1794, is 17,500 French feet long, and when it reached the town was more than 2,000 feet wide and forty feet deep. While this mighty mass of molten stone, the volume of which has been reckoned at about 457 millions of cubic feet, was descending towards the sea, another stream, whose mass is computed at about one-half of that of the former, was flowing in the direction of Mauro. This single eruption has therefore furnished more than 685 millions of cubic feet of lava, equal to a cube of 882 feet, in which at least a dozen of the largest churches, palaces, and pyramids on earth might conveniently find room. If to the solid lava we add the astonishing quantities of scoriæ, sand, and ashes thrown out by this same eruption, we may form some idea of the masses of matter which were in this one instance ejected from the interior of the earth.

The volume of the lava-stream which flowed from the volcano of the Isle of Bourbon in the year 1787 is estimated at 2,526 millions of cubic feet; but even this astonishing ejection of molten stone is surpassed by that which took place during the eruption of Skaptar Jökull[^[9]] in 1783, when the lava rolled on to a length of fifty miles, and, on reaching the plain, expanded into broad lakes, twelve and fifteen miles in diameter and a hundred feet deep.