RELICS OF PRIMEVAL LIFE

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Cryptozoon Boreale, Dawson.
Two divisions or branches of a large specimen collected by
Mr. E. T. Chambers in the Ordovician of Lake St. John.
(See Appendix D.)

[Frontis.

RELICS OF
PRIMEVAL LIFE

BEGINNING OF LIFE IN THE
DAWN OF GEOLOGICAL TIME

BY

SIR J. WILLIAM DAWSON
LL.D., F.R.S., Etc.

WITH SIXTY-FIVE ILLUSTRATIONS

NEW YORK CHICAGO TORONTO

FLEMING H. REVELL COMPANY

1897

The substance of a Course of Lectures on Pre-Cambrian Fossils
delivered in the Lowell Institute, Boston,
in November, 1895.

To

AUGUSTUS LOWELL Esq

Vice-President of the American Academy of Arts and Sciences
Trustee of the Lowell Institute

AS THE WISE AND LIBERAL ADMINISTRATOR OF A NOBLE
ENDOWMENT FOR THE ADVANCEMENT AND DIFFUSION
OF KNOWLEDGE

THIS WORK IS DEDICATED
WITH MUCH RESPECT AND ESTEEM
BY THE AUTHOR

PREFACE

I

IT is now more than thirty-five years since the announcement was made of the discovery of remains supposed to indicate the existence of animal life in the oldest rocks known to geologists. It was hailed with enthusiasm by some as "opening a new era in geological science"; but was regarded with scepticism by others, in consequence of the condition and mineral character of the supposed fossil, and because of the great interval in time between the oldest animal remains previously known and these new claimants for recognition. Since that time, many new facts have been learned, and the question has been under almost continuous discussion and debate, with various fortunes, in different quarters.

The author was associated with the original discovery and description of these supposed earliest traces of life; and has since, in the intervals of other work, devoted much time to further exploration and research, the results of which have been published from time to time in the form of scientific papers. He has also given attention to the later discoveries which have tended to fill up the gap between the Laurentian fossil and its oldest known successors.

In 1875 he endeavoured to sum up in a popular form what was then known, in a little volume named "The Dawn of Life," which has long been out of print; and in 1893 the matter was referred to in a chapter of his work "Salient Points in the Science of the Earth." In 1895 he was invited to present the subject to a large and intelligent audience in a course of lectures delivered in the Lowell Institute, Boston; and the success which attended these lectures has induced him to reproduce them in the present work, in the hope that inquiries into the Dawn of Life may prove as fascinating to general readers as to those who prosecute them as a matter of serious work, and that their presentation in this form may stimulate further research in a field which is destined in the coming years to add new and important domains to the knowledge of life in the early history of the earth.

Hypotheses respecting the introduction and development of life are sufficiently plentiful; but the most scientific method of dealing with such questions is that of searching carefully for the earliest remains of living beings which have been preserved to us in the rocky storehouses of the earth.

There are many earnest labourers in this difficult field, and it will be the object of the writer in the following pages to do justice to their work as far as known to him, as well as to state his own results.

J. W. D.

CONTENTS

APPENDIX

LIST OF ILLUSTRATIONS

Click on map to view larger sized

Walker & Boutall SCt

Grenville Series on the Ottawa River (17 miles to an inch).
From Logan's Original Map of 1865.

THE CHAIN OF LIFE TRACED BACKWARD
IN GEOLOGICAL TIME

GEOLOGICAL CHRONOLOGY OF LIFE.

After Prof. C. A. White.

See [transcription] below.

Note.—It is not supposed that the Geological Periods were of equal lengths, as represented in the diagram.

ERRATA.

Where Cryptozoon prolificum occurs in the text, read Cryptozoon proliferum.

[Transcriber Note: Errata Corrections HAVE BEEN applied to text!]

I

THE CHAIN OF LIFE TRACED BACKWARD IN
GEOLOGICAL TIME

I

IN infancy we have little conception of the perspective of time. To us the objects around us and even our seniors in age seem to have always been, and to have had no origin or childhood. It is only as we advance in knowledge and experience that we learn to recognise distinctions of age in beings older than ourselves. In thinking of this, it seems at first sight an anomaly, or at least contrary to analogy, that the oldest literature and philosophy deal so much with doctrines as to the origins of things. In this respect primitive men do not seem to have resembled children; and the fact that our own sacred records begin with answers to such questions, and that these appear in the oldest literary remains of so many ancient nations, and even in the folk-lore of barbarous tribes, might be used as an additional argument in favour of an early Divine revelation on such subjects, as a means of awakening primitive men to the comprehension of their own place in the universe.

However this may be, it is certain that modern science at first took a different stand.

The constancy of the motions of the heavenly bodies, our great time-keepers, and of the changes on the earth depending upon them, and the resolution of apparent perturbations into cycles of greater or less length, impressed astronomers and physicists with the permanence of the arrangements of the heavens and their eternal circling round without any change. In like manner, on the rise of geology, the succession of changes recorded in the earth seemed interminable, and Hutton could say that in the geological chronology he could see "no vestige of a beginning, no prospect of an end."

But the progress of investigation has changed all this, and has brought physical and natural science back to a position nearer to that of the old cosmogonies. Physical astronomy has shown that the constant emission of heat and light from the sun and other stars must have had a beginning, and is hurrying on toward an end, that the earth and its satellite the moon are receding from each other, and that even the spinning of our globe on its axis is diminishing in rapidity. In summing up these and other changes, Lord Kelvin says: "To hold the doctrine of the eternity of the universe would be to maintain a stupendous miracle, and one contrary to the fundamental laws of matter and force."

So, on our earth itself, we can now assign to their relative ages those great mountain chains which have been emblems of eternity. We can transfer ourselves in imagination back to a time when man and his companion animals of to-day did not exist, when our continents and seas had not assumed their present forms, and even when the earth was an incandescent mass with all its volatile materials suspended in its atmosphere. It is true that in all the changes which our earth has undergone the same properties of matter and the same natural laws have prevailed; but the interactions of these properties and laws have been tending to continuous changes in definite directions, and not infrequently to accumulations of tension leading to paroxysmal vicissitudes.

If all this is true of the earth itself, it is especially applicable to its living inhabitants. Successive dynasties of animals and plants have occupied the earth in the course of geological time; and as we go back in the record of the rocks, first man himself and, in succession, all the higher animals disappear, until at length in the oldest fossiliferous beds only a portion of the more humble inhabitants of the sea can be found. In the time of the formation of the oldest of these rocks, or perhaps somewhat earlier, must have been the first beginning of life on our planet.

Just as we can trace every individual animal to a microscopic germ in which all its parts were potentially present, so we can trace species, genera, and larger groups of animals to their commencement at different points of the earth's history, and can endeavour to follow the lines of creation or descent back to the first beings in which vital powers manifested themselves. All such beginnings must end in mystery, for as yet we do not know how either a germ or a perfect animal could originate from inanimate matter; but we may hope at least to make some approximation to the date of the origin of life and to a knowledge of the conditions under which it began to exist, confining ourselves for the present principally to the Animal Kingdom.

As preliminary to the consideration of this subject, we may shortly notice the grades of animals at present existing, and then the evidence which we have of their successive appearance in different periods of geological time, in order that we may eliminate all those of more recent origin, in so far as the knowledge at present available will permit, and restrict our consideration to forms which seem to have been the earliest. In attempting this, we may use for reference the table of geological periods and animal types presented in the diagram facing this chapter, which is based on one prepared by Prof. Charles A. White, of the United States Geological Survey, with modifications to adapt it to our present purpose. In this table the leading groups of animals are represented by lines stretching downward in the geological column of formations as far as they have yet been traced. Such a table, it must be observed, is always liable to the possibility of one or more of its lines being extended farther downward by new discoveries.

The broadest general division of the Animal Kingdom is into back-boned animals (Vertebrates) and those which have no back-bone or equivalent structure (Invertebrates).[1] The former includes, besides man himself, the familiar groups of Beasts, Birds, Reptiles, and Fishes. The latter consists of the great swarms of creatures included under the terms Insects, Crustaceans, Worms, Cuttle-fishes, Snails, Bivalve Mollusks, Star-fishes, Sea-urchins, Coral Animals, Sea-jellies. Sponges, and Animalcules. This mixed multitude of animals, mostly of low grade and aquatic. Includes a vast variety of forms, which, though comparatively little known to ordinary observers, are vastly numerous, of great interest to naturalists, and, as we shall find, greatly older in geological date than the higher animals.

[1] The twofold primary division now sometimes used, into Metazoa and Protozoa, seems more arbitrary and unequal, and therefore of less practical value.

It will be seen by a glance at the diagram that the higher vertebrates are of most recent origin, man himself coming in as one of the newest of all. Only the lower reptiles or batrachians and the fishes extend very far back in geological time. None of the other vertebrate groups reach, so far as yet known, farther back than the middle of the geological scale—probably in point of time very much less than this. Those of the invertebrates that breathe air reach no farther back than the fishes, possibly not so far. On the other hand, all the leading groups of marine invertebrates run without interruption back to the Lower Cambrian, and some of them still farther. Thus it would appear that for long ages before the introduction of land or air-breathing animals of any kind, the sea swarmed with animal life, which was almost as varied as that which now inhabits it. The reasons of this would seem to be that the better support given by the water makes less demands upon organs for mechanical strength, that the water preserves a more uniform temperature than the air, and that arrangements for respiration in water are less elaborate than those necessary in air. Hence the conditions of life are, so to speak, easier in water than in air, more especially for creatures of simple structure and low vital energy. Besides this, the waters occupy two-thirds of the surface of the earth, and in earlier periods probably covered a still greater area.

We are now in a position to understand that the Animal Kingdom had not one but many beginnings, its leading types arriving in succession throughout geological time. Thus the special beginning of any one line of life, or those of different lines, might form special subjects of inquiry; but our present object is to inquire as to the first or earliest introduction of life in our planet, and in what form or forms it appeared. We may, therefore, neglect all the vertebrate animals and the air-breathing invertebrates, and may restrict our inquiries to marine invertebrates.

In relation to these, six of the larger divisions or provinces of the Animal Kingdom may suffice to include all the lower inhabitants of the ocean, whether now or in some of the oldest fossiliferous rocks.[2]

[2] Some modern zoologists, having perhaps, like some of the old Greeks, lost the idea of the unity of nature, or at least that of one presiding divinity, prefer for the larger divisions of animals the term phylum or phylon, implying merely a stock, race or kind, without reference to a definite place in an ordered kosmos.

Looking more in detail at our diagram, we observe that the higher vertebrates nearest to man in structure extend back but a little way, or, with a few minor exceptions, only as far as the beginning of the Kainozoic or Tertiary Period, in the later part of which we still exist. Other air-breathing vertebrates, the birds and the true reptiles, extend considerably farther, to the beginning of the previous or Mesozoic Period. The amphibians, or frog-like reptiles, reach somewhat farther, and the fishes and the air-breathing arthropods farther still. On the other hand, our six great groups of marine invertebrates run back for a vast length of time, without any companions, to the lowest Palæozoic, and this applies to their higher types, the cuttles and their allies, and the crustaceans, as well as to the lower tribes. Turning now again to our table, we find that these creatures extend in unbroken lines back to the Lower Cambrian, the oldest beds in which we find any considerable number of organic remains, and leave all the other members of the Animal Kingdom far behind.

If now we endeavour to arrange the leading groups of these persistent invertebrates under a few general names, we may use the following, beginning with those highest in rank:—

(1) Insects and Crustaceans (Arthropoda).

(2) Cuttles, univalve and bivalve Shell-fishes (Mollusca).

(3) Worms (Annelida).

(4) Sea-urchins and Sea-stars (Echinodermata).

(5) Coral Animals, Sea-anemones, and Sea-jellies (Cœlenterata).

(6) Sponges, Foraminifera and Animalcules of simple organization (Protozoa).

There are, it is true, some animals allied to the mollusks and worms, which might be entitled to form separate groups, though of minor importance The position of the sponges is doubtful, and the great mass of Protozoa may admit of subdivision; but for our present purpose these six great groups or provinces of the Animal Kingdom may be held to include all the humbler forms of aquatic life, and they keep company with each other as far as the Early Cambrian. If, in accordance with the previous statements, we choose to divide the earth's history by the development of animal life rather than by rock formations, and to regard each period as presided over by dominant animal forms, we shall thus have an age of man, an age of mammals, an age of reptiles and birds, an age of amphibians and fishes, and an age of crustaceans and mollusks.

It is only within recent years that the researches more especially of Barrande, Hicks, Lapworth, Linarrson, Brögger, and others in Europe, and of Matthew, Ford and Walcott in America, have enlarged the known animals of the Lower Cambrian to nearly 200 species, and below this we know as yet very little of animal life. We may therefore take the Lower Cambrian, or "Olenellus Zone" as it has been called from one of its more important crustaceans,[3] as our starting-point for plunging into the depths below. In doing so, we may remark on the orderly and symmetrical nature of the chain of life, and on the strange fact that for so long ages animal life seems to have been confined to the waters, and to have undergone little development toward its higher forms. It is like a tree with a tall branchless stem bearing all its leaves and verdure at the top, or like some obscure tribe of men long living in isolation and unknown to fame, and then, under some hidden impulse or opportunity, becoming a great conquering and dominant nation. Or to compare it with higher things, it is like the Christian religion, for ages confined to a small and comparatively unimportant people, and developing slowly its faith and hopes, and then suddenly, under the personal influence of Christ and His apostles, spreading itself over the world, and in a few centuries becoming the ruling power in its greatest empire, surviving the fall of this and permeating all the great nations that sprang from its ruins. God's plans in nature, in history, and in grace seem to us very slow in their growth and maturity, but they are very sure.

[3] See figure, [p. 20].

LIFE IN THE EARLY CAMBRIAN

II

LIFE IN THE EARLY CAMBRIAN

I

IN the old Chaldean fable of the descent of Ishtar into Hades, to recover her lost Tammuz, at each successive gate of the lower regions she is stripped of some of her ornaments and garments, till at length she has to appear naked and unadorned in the presence of the lord of the Nether World. So in our descent from the surface on which men live, through the successive rocky layers of the earth's crust, we leave behind, one by one, all the higher forms of life with which we are familiar; but there still remain to us our six groups of aquatic invertebrates, in the guise, it is true, of species and genera now unknown in a living state, yet well represented as far down as the lower part of the Cambrian. Let us now suppose that we take our stand on the shores of the Cambrian sea, or cast our dredge into its waters in search of these old animals; though we can only actually do so by painfully hammering and chiselling them out of their rocky tombs, and this often in fragments which must be put together before we can fully realize the forms and structures of the animals to which they belonged.

We may pause here, however, to remark that neither the geographical nor climatal conditions of the earth at this early time were similar to these with which we are now familiar. The marine animals of the Cambrian have left their remains in beds of sediment, which now constitute rocks forming parts of our continents remote from the sea, and much elevated above its level, showing that large areas, then under the ocean, are now dry land; while there is no good evidence that the sea and land have changed places. The facts rather indicate that the continents have extended their area at the expense of the ocean, which has, however, probably increased in depth. In evidence of these statements, I need only mention that some of the oldest rocks in the Scottish and Welsh hills, in Scandinavia, in Russia and in Bohemia, are rich in Cambrian marine fossils.

Fig. 1.—Olenellus Thompsoni, Hall.
A characteristic Trilobite of the Lower Cambrian in North America. After Walcott and specimen in Peter Redpath Museum.

In America, in like manner, such rocks are found on the flanks of the Appalachians, in New Brunswick, and in Newfoundland, in the table-land of Colorado and in the Rocky Mountains. In point of fact, a map of the Northern Hemisphere at this period would show only a limited circumpolar continent with some outlying islands to the south of it, and shallows stretching across the northern part of the areas of the present Atlantic and Pacific Oceans. The great ocean, however, thus extending over most of the temperate and tropical parts of the Northern Hemisphere, was probably also more muddy and shallow than that of modern times. The surface temperature of this vast ocean was also, it is probable, more uniform than that of the modern sea, while even its profounder depths or abysses would have more earth-heat than at present. Thus we may, without hesitation, affirm that in this early age the conditions for the introduction of swarming marine life of low grade, and its extension over the whole earth, were at a maximum.

Let us inquire, then, what these old Cambrian seas actually produced, more especially in the early portions of that ancient and probably protracted time.

The most highly organized type of which we have any certain evidence is that of the Crustacea, the group to which our modern lobsters and crabs belong, and its most prominent representatives are the trilobites (Figs. [1], [2]), so called from the three lobes into which the body is divided. These creatures are indeed remarkable for the twofold property of bilateral symmetry, and fore and aft jointed structure, both based on the number three. From front to rear we have a large head, usually with well-developed eyes and oral organs, a middle or thoracic part composed of a series of movable segments, and a tail-piece sometimes small, sometimes nearly as large as the head. Transversely, the body is divided into a central and two lateral lobes, which can be seen in the head, the thorax, and usually in the tail as well. The organization of these animals must have been as complex as that of most existing Crustaceans. Their nerve system must have been well developed; a vast number of muscles were required to move the different parts of the trunk, and the numerous and complex limbs which have been observed in some of the species, and no doubt were possessed by all. Their digestive and circulatory organs must have been in proportion to the complexity of their locomotive organs.

Fig. 2.—Triarthrus Becki, Green.
A Trilobite of primitive type, showing its limbs and antennæ. (After Beecher.)

Figure 2, borrowed from Beecher,[4] shows the limbs of a species, not of the Lower Cambrian, but of a somewhat later formation. There can be no doubt, however, that those of earlier species were equally perfect, more especially as Triarthrus is an animal of an old type approaching to extinction in the age succeeding the Cambrian, and its representatives in the earlier and palmy days of the family could not have been inferior in organization. These creatures swarmed in every sea in the Cambrian period, and were represented by a great number of species, some of them of large size, others very small; some many-jointed, others few-jointed, and with a great variety of tubercles, spines, and other ornamental and protective parts. If we ask for their affinities and place in the great group of Crustacea, the answer must be that, while in some points allied to the higher forms, they approach most nearly to those which occupy a medium position in the class, and are, in fact, a composite type, presenting points of structure now distributed among different groups. If we ask for affinities with lower groups, we have to reply that their nearest allies in this direction are the bristle-footed marine worms; but there is a vast gap, both in the Cambrian and Modern seas, between any of these worms and the Crustacea, which, either as embryos or as adults, have any resemblance to them.

[4] American Journal of Science, 1896.

The Trilobites, after appearing in a great variety of generic and specific forms, and playing a most important part in their time, were not destined to continue beyond the Carboniferous period, and before that time they were beginning to give place to the Limuli, King-crabs, or Horseshoe-crabs, a few species of which continue on our coasts until the present time. In this limited duration the Trilobites present a strange contrast to certain shrimp-like Crustaceans, their contemporaries (the Phyllopods), which very closely resemble some still extant, and the same remark applies to swarms of little bivalve Crustaceans (Ostracods), which are still represented by hosts of modern species both in the sea and in the fresh waters. There is, however, a remarkable group of shrimp-like Crustaceans, represented in the modern world by only a few small species, which in the Cambrian age attained greater size, and constitute a very generalized type combining characters now found in lower and higher groups of Crustacea.

Hymenocaris vermicauda of Salter ([Fig. 3]) may serve to illustrate one of these primitive forms.

Fig. 3.—Hymenocaris vermicauda, Salter.
A Lower Cambrian Shrimp of generalized type. (After Salter.)

In point of fact, as Dr. Henry Woodward has shown in an able presidential address delivered to the Geological Society in 1895, at the base of the Lower Cambrian we still have several distinct groups of Crustacea; and if with some we were to hold them as traceable to one original form or to a worm-like ancestor, we must seek for this far back in those pre-Cambrian rocks in which we find no Crustaceans whatever. There is, it is true, no good reason to demand this; for whatever the cause, secondary or final, which produced any form of Crustacean in the Lower Cambrian, it might just as well have produced several distinct forms. Evolutionists seem to be somewhat unreasonable in demands of this kind, for any cause capable of originating a new form of living being, might have been operative at the same time in different localities and under somewhat diverse conditions, and may also have acted at different times. All imaginary lines of descent of animals are more or less subject to this contingency; and this may partly account for the great diversity in the lines of affiliation presented to us by evolutionists, which may in part have a basis in fact in so far as distinct varietal and racial forms are concerned, but may just as likely be entirely fallacious in the case of true species. In any case, in the lowest rocks into which we can trace Crustacea, we have already probably five of the orders into which their successors in the modern seas are divided by zoologists; and this is certainly a singular and suggestive fact, the significance of which we shall be better prepared to understand at a later stage of our investigation.

Allied in some respects to the Crustacea, though much lower in grade, are the marine Worms—a great and varied host—usually inhabiting the shallower parts of the ocean; though the 330 species collected by the Challenger expedition show that they also abound in those greater depths to which voyagers have only recently had access. Sea-worms seem thus to be able to live in all depths, as well as in all climates; and in accordance with this they abound in the oldest rocks, which are often riddled with the holes caused by their burrowing, or abundantly marked on the surfaces of the beds with their trails.

The great province of the Mollusca, in which, for our present purpose, we may include some aberrant and rudimentary Molluscoids, is now best known to us by its medium types, the univalve and bivalve Shell-fishes; the higher group of the Cuttle-fishes and Nautili, though not uncommon, being much less numerous, and one at least of the lower groups, the Lamp-shells or Brachiopods, being represented in the modern world by but few forms. The extension of the Mollusks backwards into the Cambrian is remarkable as being on the whole meagre in comparison with that of the Crustaceans, and as presenting only in small numbers the types most common in later times. One or two shells, and perhaps some tracks, represent the highest group: some forms resembling the floating species of Sea-snails, and a very few ordinary bivalves represent the types best known in the modern seas; while the Brachiopods, and probably some still simpler forms, are in great comparative excess. The individual specimens are also of small size, as if these creatures were but insinuating themselves on the arena of life in insignificant and humble forms. So far as yet known, the lowest groups supposed to be allied to the Mollusks, the Ascidians or Sea-squirts, and the Sea-mosses (Polyzoa), do not appear; but they may have been represented by species which possessed no hard parts capable of preservation.

This leads us to the consideration that while all the Crustacea necessarily possess some kind of crust or external skeleton, the Mollusks are very different in this respect. While some of them have ponderous shells, others even of the highest forms are quite destitute of such protective parts. This again leads to a curious question respecting the armature of the Trilobites. Some of these, even of the larger species, have strong and formidable spines, like those of the King-crabs and other modern Crustaceans. Now in the modern species we know these organs to be intended to defend their possessors against the attacks of fishes more swift and powerful than themselves. But what enemies of this kind had the Trilobites to dread? Yet species a foot or more in length presented great bayonet-like spines.

Fig. 4.—Ctenichnites ingens, Matthew.
A slab with markings of aquatic animals. From specimen in Peter Redpath Museum.

All that we know on this subject is that on the surfaces of the Lower Cambrian rocks there are in some places complicated and mysterious tracks or scratches, which seem to have been produced when the rock was in the state of soft mud, by large and swiftly swimming animals possessing some sort of arms or similar appendages ([Fig. 4]). Matthew has ingeniously suggested that they may have been large Mollusks allied to the modern gigantic Squids which still abound in the ocean, that they may have been sufficiently powerful to prey on the Trilobites, and, being swift swimmers, would have found them a helpless prey but for their defensive spines. Yet such large Mollusks might have perished without leaving any remains recognisable in the rocks, except what may be termed their hand-writing on clay. A few small examples of the shell-bearing species of these highest Mollusks, however, appear in the Cambrian, and in the succeeding ages they become very abundant and attain to large dimensions, again dwindling toward modern times. It would thus seem that for some unknown reason the highest and lowest Mollusks may have been locally plentiful, but the intermediate types were rare.

The much lower group of Echinoderms, or Sea-urchins and Sea-stars, curiously enough puts in but a small appearance in the Early Cambrian, being represented, as far as yet known, by only one embryonic group, the Cystideans. A little later, however, Feather-stars became greatly abundant, and a little later still the true Star-fishes and Urchins. The aberrant group of the Sea-slugs seems, so far as known, to be of more modern origin; but most of these animals are soft-bodied, and little likely to have been preserved.

The great group of the coral animals, so marked a feature of later ages, is scarcely known in the oldest Cambrian, except by some highly generalized forms[5] ([Fig. 5]). There are, however, small Zoophytes referable to the lower type of Hydroids, and markings which are supposed to be casts of stranded Jelly-fishes. If, with some naturalists, we regard the Sponges as very humble members of the coral group (Cœlenterata), then we have a right to add them to its representatives in the lowest Cambrian; but perhaps they had better be ranked with the next and lowest group of all—the Protozoa.

[5] Dr. G. J. Hinde has carefully studied these forms, and also similar species occurring in Lower Cambrian beds in different parts of North America, Spain, Sardinia, and elsewhere. See note in the Appendix, and Journal Geol. Society of London, vol. xlv. p. 125.

Fig. 5.—Archæocyathus profundus, Billings.
Possibly a Coral of generalized type from the Lower Cambrian of L'Anse à Loup, Labrador. A small specimen.

Fig. 6.—Structures of A. profundus (magnified).
From specimens in Peter Redpath Museum.
(a) Lower acervuline portion. (b) Upper part, with three of the radiating laminæ and section of pores, (c) Portion of lamina, with pores, the calcareous skeleton unshaded.

These are the humblest of all the inhabitants of the sea, presenting very simple, jelly-like bodies with few organs, but sometimes producing complex and beautiful calcareous and siliceous coverings or tests. Animals of this type have been found in the Lower Cambrian, though not in such vast multitudes as in some later formations. There are also in the Cambrian some large, laminated, calcareous bodies (Cryptozoon of Hall), to be noticed more fully below, and which have recently been traced in still lower deposits even below the lowest Cambrian (Figs. [7], [8]). These have some resemblance to the layer-corals or stromatoporæ of the Silurian and Ordovician, which are by many regarded as the skeletons of coral animals of a low type; but the microscopic structure of Cryptozoon rather allies it with some of the larger forms of Protozoa found higher up in the series of formations. We shall have to discuss this later in connection with still older fossils.

Fig. 7.—Cryptozoon proliferum, Hall.
Portion of slab reduced in size. (After Hall.) See also [Fig. 59, p. 237].

Fig. 7a.—Portion of thin section of Cryptozoon proliferum (magnified × 50).
(a) Corneous layers, (a¹) One of these dividing, (b) Intermediate stroma with granules of calcite, dolomite and quartz, traversed by canals.
From a Micro-photograph by Prof. Penhallow.

[To face p. 39.

If now in imagination we cast our tow-net or dredge into the sea of the Lower Cambrian, we may hope to take specimens illustrative of all our six groups of invertebrate animals, and under several of them examples of more than one subordinate group. Of the Crustaceans we might have representatives of four or five ordinal groups, and of the Mollusca as many. These are the two highest and most complicated. In the four lower groups we would naturally have less variety, though it would seem strange, were it not for so many examples in later periods, that the dominant and highest groups should be most developed in regard to the number of their modifications.

Fig. 8.—Diagrammatic section of two Laminæ of Cryptozoon, showing the Canals of the intermediate space, or Stroma (magnified).
Specimen in Peter Redpath Museum.

Of the whole we might perhaps have been able to secure at least 200 species even in one locality. The likelihood is that if there had been a collecting expedition like that of the Challenger in Early Cambrian times, it could have secured thousands of specific forms representing all the above types, more especially as we probably know very little of the softer and shell-less animals of these old seas, and there is some reason to believe that these may have been in greater proportion than in the present ocean.

In illustration of the richness of some parts of the lowest Cambrian sea, I may refer here to the large and beautifully illustrated Memoir of Walcott on the Lower Cambrian, containing fifty folio plates of species collected in a few districts of North America; and, as a minor example, to the contents of a loose boulder of limestone of that age, found at Little Metis on the Lower St. Lawrence, under the following circumstances ([Fig. 9]):—

Fig. 9.—Lower Cambrian Fossils found in a few cubic inches of limestone in a conglomerate at Little Metis; viz., Trilobites of genera Olenellus, Ptychoparia, Solenopleura, Protypus; Brachiopod of genus Iphidea; Pteropod of genus Hyolithes; Gastropod, genus Stenotheca; Sponge, undetermined.

Along what is now the valley of the Lower St. Lawrence and the gulf of the same name, there seem to have been deposited in the oldest Cambrian or Olenellus period beds of limestone rich in shells of marine animals and fragments of these. These can be seen in place in some parts of Newfoundland, and here and there on the hills bounding the St Lawrence River; but for the most part they have been swept away by the sea when these districts were being elevated to form parts of the American land. Their ruins appear as boulders and pebbles in thick beds of conglomerate or pudding-stone, constituting portions of the Upper Cambrian and Lower Ordovician series, which now occupy the south coast of the Lower St. Lawrence. In one of these boulders, less than a foot in diameter, removed from its hard matrix and carefully broken up, I found fragments representing eleven different species, of which no less than eight were trilobites, one a gastropod, one a brachiopod, and one probably a sponge—and this forms an interesting illustration of the number of species sometimes to be found in a limited space, and also of the great prevalence of the Trilobites in these beds. The statistics of these groups for North America, as given by Walcott, show 165 species belonging to all the groups enumerated above, and of these the Trilobita constitute one-third of the whole; so that the Olenellus Zone, as it has been called from one genus of these Crustaceans, might well be named the reign of Trilobites, unless, indeed, as the indications already referred to seem to show, giant cuttle-fishes, destitute of shells, were then the tyrants of the sea, but are represented only by the markings of their long and muscular arms on the soft sea mud while dashing after their Crustacean prey. What I desire, however, chiefly to emphasize is, that in the lowest beds of the Cambrian we have evidence of sea-bottoms swarming with representatives of all the leading types of marine invertebrate life, and therefore seem to be still far from the beginning of living things, if that was a slow and gradual process, rather than a sudden or rapid series of events.

PRE-CAMBRIAN LIFE

III

PRE-CAMBRIAN LIFE

H

HAVING traced the chain of life through the long geological ages, from the present day back to the Cambrian Period, we may now take our stand on the fauna of the lowest Cambrian or Olenellus Zone, as a platform whence we may dive into still deeper abysses of past time. Here, however, we seem to have arrived at a limit beyond which few remains of living things have yet been discovered, though there still remain pre-Cambrian deposits of vast thickness and occupying large areas of our continents. These pre-Cambrian formations are as yet among those least known to geologists. The absence of fossils, the disturbances and alterations which the rocks themselves have undergone, and which make their relative ages and arrangement difficult to unravel, have acted as deterrents to amateur geologists, and have to some extent baffled the efforts of official explorers. In addition to this, workers in different regions have adopted different methods of arrangement and nomenclature; and in a very recent address, the Director-General of the Geological Survey of Great Britain expresses his inability to satisfy himself of the equivalency of the different pre-Cambrian groups on the opposite sides of the Atlantic, and in consequence prefers to retain for those of Britain merely local names.

On the other hand, those who hold the modern theories of gradual evolution repudiate the idea that the Lower Cambrian fauna can be primitive, and demand a vast series of changes in previous time to prepare the way for it. In any case this comparatively unexplored portion of geological time holds out the inducement of mystery and the possibility of great discoveries to the hardy adventurers who may enter into it. It must now be our effort to explore this dim and mysterious dawn of life, and to ascertain what forms, if any, are visible amid its fogs and mists.

The Kewenian or Etcheminian.

In certain basal Cambrian or infra-Cambrian beds, found by Matthew in Southern New Brunswick, by Walcott in Colorado, and by Scandinavian and English geologists in their respective countries, we find a few remains referred to Algæ, or seaweeds; small tests or shells of Protozoa; burrows and trails similar to those of modern sea-worms; a few bivalve shells allied to modern Lingulæ, but presenting some remarkable generalized characters; some bivalve and shrimp-like Crustaceans, spicules of sponges, and large laminated forms (Cryptozoon) similar to those already referred to as occurring in the Upper Cambrian; also certain mysterious markings that are supposed to have been produced by the arms or tentacles of free-swimming animals of various kinds. In these lower beds the Trilobites have nearly or quite disappeared, being represented only by doubtful fragments. The beds of rock, originally sandy or muddy sediments, contain fossils very sparingly, and only in certain layers separated by great thicknesses of barren material, as if earthy matters were being deposited very rapidly, or as if animal life was rare on the sea-bottom except at intervals. It has, however, been suggested as possible[6] that much of the marine population in those early times consisted of pelagic or swimming animals destitute of any hard parts that could be preserved. In addition to biological arguments in favour of this view, there is the fact that some of the beds are stained with carbonaceous or coaly matter, as if the sediment had been mixed with decomposed remains of plants or animals retaining no determinate forms. Future discoveries may increase our knowledge of the life of this period preceding the Cambrian, but it is evident that so far as these rocks have been examined, they indicate a great step downward in regard to the variety and complexity of marine life.

[6] By Prof. Brookes, of Johns Hopkins University.

Still we must bear in mind that in later periods there have been times of rapid deposition, in which, in certain localities at least, great thicknesses of rock with few organic remains were formed. We have instances of this in the later Cambrian, in the Ordovician, and still later in the Permian and Trias. Thus in the beds immediately underlying the lowest Cambrian we may be passing through a tract of comparative barrenness to find more fertile ground below.

It is also to be observed that there is evidence of disturbance occurring in the interval between the lowest Cambrian and the highest pre-Cambrian, which may involve the lapse of much time not recorded in the localities hitherto explored, but of which monuments may be found elsewhere.

We may now, taking some North American localities as our best available guides, inquire as to the nature and contents of the beds next below the Lower Cambrian.

Fig. 10.—Section at Hanford Brook. (After Matthew.)
Showing St. John group resting on Etcheminian, and this on Coldbrook (Huronian).

In Southern New Brunswick, Matthew indicated, several years ago, the occurrence of certain conglomerates and sandy and slaty beds over the rocks, mostly of igneous origin, constituting a great thickness of beds under the Cambrian, and known locally as the "Coldbrook" series, which is probably equivalent to the Huronian of Northern and Western Canada, to be noticed later. These beds were at first regarded as an upper member of the Huronian, but subsequently it was thought better to unite them with the overlying Cambrian as basal Cambrian. The fact that these problematical beds were ascertained to be unconformable to the Cambrian, and the peculiarity of their fossils, led to their being constituted a separate group under the name Etcheminian, which seems to represent a time and conditions introductory to the Cambrian ([Fig. 10]). The fossils in these beds are few and hard to find. Matthew has kindly furnished me with the following list.[7] The Trilobites are conspicuous by their absence. Sea-worms have left burrows, trails, and casts, which probably represent several species ([Fig. 11]). A single little shell (Volborthella) is supposed to be a precursor of the straight chambered shells allied to the modern nautilus, which become so large and numerous in succeeding periods. There are a few univalve shell-fishes allied to modern sea-snails, a brachiopod of the antique genus Obolus, some fragments supposed to represent Cystideans, a rudimentary type of the stalked sea-stars so abundant later, spicules of sponges and minute Protozoa, with shells not unlike those of their modern successors. This meagre list sums up the forms of life known in the Etcheminian of this district, one in which the Cambrian beds exhibit the rich and varied fauna of Trilobites and other animals described and figured by Matthew in several successive volumes of the "Transactions of the Royal Society of Canada" ([Fig. 12]).

[7] "Transactions Royal Society of Canada," vol. vii.

Fig. 11.—Trails of Worms of two types (Psammchnites and Planilites).

Beds in Newfoundland (the Signal Hill and Random Sound series), underlying the Lower Cambrian, have afforded to Murray and Billings some well-characterized worm-castings of spiral form, and a few problematical forms known as Aspidella, which may be Crustaceans or Mollusks allied to the limpets ([Fig. 13]).

Fig. 12.—Group of pre-Cambrian (Etcheminian) Animals from the Etcheminian. (After Matthew.)
The name "Etcheminian" is derived from that of an ancient Indian tribe of New Brunswick.
(a) Volborthella, supposed to be a Cephalopod shell. (b) Pelagiella. (c) Orthotheca, supposed to be Pteropods. (d) Primitia, an Ostracod Crustacean, (e) Obolus, a Brachiopod shell. (f) Platysolenites, probably fragment of a Cystidean. (g) Globigerinæ, casts of Foraminiferal shells, Etcheminian, New Brunswick.

Fig. 13.—Arenicolites (Spiroscolex) spirales (Billings) and Aspidella tenanovica (Billings), Signal Hill Series, Newfoundland.

Fig. 14.—Fragment of Cryptozoon, Grand Cañon, Arizona.
Photograph from a specimen presented by Dr Walcott to the Peter Redpath Museum.

In a thick series of pre-Cambrian beds in the Colorado Cañon in the Western United States, Walcott has found a small roundish shell of uncertain affinities,[8] a species of Hyolithes, probably a swimming sea-snail or Pteropod, a small fragment which may possibly have belonged to a Trilobite, and some laminated forms which, if organic, are related to the Cryptozoon already mentioned ([Fig. 14]).

[8] Discinoid or Patelloid.

The Kewenian series of Lake Superior has yielded no fossils, but the pipestone beds of Minnesota, supposed to be about the same age, have afforded a small bivalve shell allied to Lingula;[9] and the black shales of the head of Lake Superior contain some impressions supposed to be trails of animals.[10]

[9] Winchell.

[10] Selwyn and Matthew.

It has been a question whether the beds above referred to should be regarded as a downward continuation of the Cambrian, or as the upper part of an older system. Matthew, whose opinion on such a subject is of the highest authority, regards them as a distinct system, but as belonging, with the Cambrian, to the great Palæozoic Period. Van Hise, and some other United States authorities, would separate them even from the Palæozoic, and unite them with the underlying Huronian, as representing a "Proterozoic" or "Algonkian" Period. This is merely a matter of classification, necessarily more or less arbitrary; but I believe the facts to be stated subsequently show that it will be best to unite the Etcheminian and its equivalents with the Palæozoic, and to place the groups lower than this in one great division, equivalent to Palæozoic, and for which many years ago I proposed the name "Eozoic," or that of the Dawn of Life.

Having thus hastily glanced at the slender fauna of the rocks immediately below the Cambrian, we may now proceed to inquire a little more in detail into its true value and import as leading toward the beginning of life. I have already referred to the apparently sudden drop in the number of groups and of species below the base of the Cambrian, and have hinted that this may be an effect of temporary local conditions of deposit or of defective information. Another fact that strikes us is the diverse and miscellaneous character of the fossils that remain to us; and this would suggest that we are either dealing with a mere handful picked at random, as it were out of a richer fauna, or that in the beginning of things the gaps and missing links between different forms of life were even more pronounced than at present. This, however, would be likely to occur if the plan of creation was to represent at first different types, with few forms in each; to produce, in short, a sort of type collection representing the whole range of organization by a few characteristic things rather than to give a complete series, with all the intermediate connections. Such a mode of introduction of life is not à priori improbable, however at variance with some prevalent hypotheses.

Beginning with the higher Invertebrates, we must not conclude that we have altogether lost the Trilobites. The fragments referred to this group may represent at least a few species, and it would be very interesting to know more of these as to their relations to their successors, and whether they are tending to lower or more embryonic forms. The bivalve Crustaceans (Ostracods) may be regarded as inferior in rank to the Trilobites, but are still very complex, and specialized animals and a specimen silicified in such a manner as to show the interior organs testified that, as far back as the Carboniferous at least, these creatures were as highly organized as at present,[11] while their generally larger size in the earlier formations tends to show that they have rather been degenerating in the lapse of geological time.

[11] Palæocypris Edwardsi, Brougniart, Coal Formation of St. Etienne, France.

In regard to the Sea-worms, the burrows, castings, and trails found in the pre-Cambrian beds are scarcely, if at all, different from those now seen on sandy and muddy shores, and would seem to indicate that these highly organized and very sensitive and active creatures swarmed in the muddy bottom of the pre-Cambrian Sea, and lived in the same way as at present. It is impossible, however, to know anything of the internal structures of these creatures, but the marks left by their bristle-bearing feet seem to indicate that some of them at least belong to the higher group of Sea-centipedes, creatures rivalling the Crustaceans in complexity of organization, and near to them in plan of structure, though at present usually widely separated from them in current systems of classification. In the Ordovician system, next above the Cambrian, Hinde has found many curiously formed jaws of animals of this kind, which show at least that their alimentary arrangements were similar to those now in force. If any of the problematical "Conodonts" discovered by Pander in the Cambrian of Russia belonged to marine worms, this inference would be extended back to the Lower Cambrian, so that if the evidence of structure anywhere remains we may hope to find that the pre-Cambrian worms were not inferior to their more modern successors, perhaps even that in this early period, when they probably played a more important part in nature, they were of higher organization than in later times.

The evidence as to pre-Cambrian mollusks, so far as it goes, is even more curious. The little shell called Volborthella, so far as can be judged from its form and internal structure, is a miniature representative of these straight Nautili, the Orthoceratites of the Ordovician and later Palæozoic rocks; and no one doubts that these latter belong to the highest class of the Mollusks, a class approaching in the development of nerve system and sensory organs to the Vertebrates themselves. This tiny member of the great class of Cuttle-fishes may perhaps have been more nearly allied to the modern Spirula than to the Nautilus. In any case, if, as seems altogether probable it was, a mollusk, it must have been one of advanced type, and with a highly complex structure, as well as the singular apparatus for flotation implied in a chambered shell with a siphuncle.

Next to this among these primitive Mollusks are straight and spiral shells representing those delicate and beautiful animals of the modern seas, the Pteropods, or wing-footed Sea-snails, beautiful and graceful creatures, the butterflies of the sea, and moving in the water with the greatest ease and beauty by the aid of membranous fins, or wings, sometimes brightly coloured. These creatures abound in all latitudes in the modern ocean, and their delicate shells sometimes accumulate in beds of "Pteropod sand." They very early entered on the arena of marine life, and have continued to this day.

We miss here the two great Molluscan groups of the creeping Sea-snails like the limpet and whelk, and of the ordinary bivalves like the oyster and cockle. Both are present in the lowest Cambrian, though in small numbers compared with their present abundance. Possibly they had not yet appeared in the Etcheminian Sea, though the muddy and sandy bottoms, evidenced by its slates and sandstones, would seem to have afforded favourable habitats, and warrant the expectation that species may yet be found.

The case was different with the little group of the Lamp-shells, or Brachiopods. These creatures, somewhat resembling the ordinary bivalves in their shelly coverings, were very dissimilar in their internal structure, and once settled on the bottom they were attached for life, not having even the limited means of locomotion possessed by the Sea-snails and common bivalves. They collected their food wholly by means of currents of water produced by cilia, or movable threads, on arms or processes within their shells. In this they resembled the young or embryo stages of some of the more ordinary Mollusks, though they are so remote from these in their adult condition that they have usually been placed in a distinct class, and some naturalists have thought it best to separate them from the Mollusks altogether. Their history is peculiar. Coming into existence at a very early date, they became very abundant in early Palæozoic times, then gradually gave place to the ordinary bivalves, and in the modern seas are represented by very few species. Yet while in the middle period of their history they are represented by very many peculiar specific and generic forms. Some of the earliest types, like Obolus and Lingula, persist very long, and the latter has continued without change from the Early Cambrian to the Modern period.

The great group of the Sea-stars and Sea-urchins appears only in a few of its lower forms, and seems to be the only class represented by embryonic types. The coral animals are absent, so far as known. The Jelly-fishes and their allies cannot be preserved as fossils, but some peculiar markings, at one time regarded as plants, are now supposed to be trails made by the tentacles of creatures of this kind moving over muddy bottoms. A few spicules indicate Sponges, and the ubiquitous groups of the marine Protozoa, the Foraminifera and the Radiolaunus, are represented by shells scarcely distinguishable from those of modern species. The great and peculiar forms represented at this early time by Cryptozoon and its allies seem long ago to have perished, and we shall have to return to them in a later stage of our inquiry.

To sum up the little that we know of this earliest Palæozoic life:—It was perfect of its kind, equally pregnant with evidences of design, and of the nicest and most delicate contrivance as the animal life of any later time, and it presupposed vegetable life and multitudes of minute organic beings altogether unknown to us to nourish the creatures we do know. As an example of this, a little Brachiopod or sponge nourished by the currents produced by its cilia, or a Jelly-fish gathering food by its thread-like tentacles, or a Globigerina selecting its nourishment by its delicate gelatinous pseudopods, required an ocean swarming with minute forms of life, which probably can never be known to us, but every one of which must have been an inscrutable miracle of organization and vital function.

Lastly, with reference to our present subject, the Etcheminian fossils carry life backward one whole great period earlier than the Lower Cambrian, and appear to indicate that we are approaching a beginning of living things in the Palæozoic world. Much no doubt remains to be discovered, but it would seem that any future discoveries must fail to negative this conclusion.

The Huronian.

In whatever way the rocks immediately below the Cambrian may be classified, it is certain that the next system in descending order is that to which Logan long ago gave the name Huronian, from its development on Lake Huron[12]—a name to which it is still entitled, though there may, perhaps, be some grounds for dividing it into an upper and lower member.[13] To this sub-division, however, we need not for the present give any special attention. In the typical area of Lake Huron the Huronian consists of quartzites, which are merely hardened sandstones, of slates which are muddy or volcanic-ash beds, of conglomerates or pebble-rocks, and of coarse earthy limestone. With these rocks are deposits of igneous material which represent contemporary volcanic eruptions. In other districts, as in New Brunswick, Newfoundland, etc., the beds have been considerably altered, and are locally more mixed with igneous products. The physical picture presented to us by the Huronian is that of a shore deposit, formed under circumstances in which beds of pebbles and sand were intermixed with the products of neighbouring volcanoes.

[12] Dr. G. M. Dawson, F.R.S., the present Director of the Geological Survey of Canada, whose judgment in this matter should be of the highest value, holds that the original simple arrangement of Logan still holds, notwithstanding the multitude of new names proposed by the Western Geologists of the United States.

[13] Van Hise, "Pre-Cambrian Rocks of North America." Comptes Rendus, 5th Session International Geol. Congress 1891, p. 134. Also "Report U.S. Geol. Survey, 1895."

Fig. 15.—Annelid Burrows, Hastings Series, Madoc.
1. Transverse section of Worm-burrow—magnified, as a transparent object. (a) Calcareo-silicious rock. (b) Space filled with calcareous spar, (c) Sand agglutinated and stained black. (d) Sand less agglutinated and uncoloured. 2. Transverse section of Worm-burrow on weathered surface, natural size. 3. The same, magnified.

Such a formation is not likely to afford fossils in any considerable number and variety, even if deposited at a time of abundant marine life. It is therefore not wonderful that we find little evidence of living beings in the Huronian. In Canada I can point to nothing of this kind, except a few cylindrical burrows, probably of worms ([Fig. 15]), and spicules possibly of silicious sponges, which occur in nodules of chert in the limestones, traces of laminated forms like Cryptozoon or Eozoon ([Fig. 17]), and minute carbonaceous fragments which may be debris of sea-weeds or Zoophytes. In rocks of similar age in the United States, Gresley has recently discovered worm-burrows, and in Brittany there are quartzite beds in which Barrois and Cayeux believe that they have found tests of Radiolarians, Foraminifera and spicules of sponges, but their organic nature has been denied by Rauff, of Bonn. The casts of Foraminifera, however, at least appear to be organic ([Fig. 16]), and it is quite likely that Cayeux may be able to verify his Radiolarians and sponges as well. Matthew's observations in New Brunswick in any case establish their probability. Gümbel also recognises a species of Eozoon in the equivalent rocks of Bavaria (see [p. 213]).

Fig. 16.—Casts of Foraminifera, from the Huronian of Brittany. (After Cayeux.)
Compare with Globigerinæ on [Fig. 12] and Archæospherinæ, Figs. [50]-[54].

Fig. 17.—Cryptozoon or Eozoon from the Hastings Series, Tudor, Ontario (natural size).
From a specimen collected by the late Mr. Vennor, and now in the collection of the Geological Survey, Ottawa. (See also Frontispiece and figure of Eozoon Bavaricum, [p. 213].)

It is evident that here we have approached the limit of the higher forms of marine invertebrate life, having as yet nothing to show except worms and Protozoa. It is to be observed, however, that there may be somewhere Huronian deposits formed in deep and quiet waters, which may give better results, and that the unconformity between the Huronian and overlying Kewenian may indicate a lapse of time, of which monuments may yet be found.

The Laurentian.

Last of all we have the widely distributed Laurentian system of Logan, the oldest known to geologists, and which with the Huronian constitutes the great Archæan group of formations of Dana and others. In its lowest part this consists entirely of the stratified granitic rock known as gneiss, inter-bedded in some places with dark-coloured crystalline rocks or schists. This may be a part of the first-formed crust of our globe, produced under conditions different from those of any later rocks, and incompatible with the existence of life. The upper part of the Laurentian system, however, known in Canada as the "Grenville Series," shows evidence of ordinary marine deposition in quiet waters, which may have been not unfavourable to the lower forms of marine life; and though its beds have been greatly changed by heat and pressure, we can still to some extent realize the conditions of a time of comparative quiescence intervening between the underlying Lower Laurentian and the succeeding Huronian. This part of the system still contains gneisses, bedded diorites, and other rocks which may have been volcanic; but it has also quartzites and quartzose gneisses which must have been sandstones or shales, thick limestones, beds of carbon now in the state of graphite or plumbago, and large beds of iron ore. Such rocks were in all succeeding formations produced under water and by accumulations of the remains of plants and the hard parts of animals, in strictly sedimentary beds, usually formed slowly and without mechanical disturbance. Hence we may infer that aquatic life at least existed in this early period, and as there must have been land and water, shallows and deep seas, there may have been scope for various kinds of living beings. The Grenville period is, however, separated from the succeeding Huronian by a great interval, occupied mainly by volcanic ejections and earth-movements; so that our Grenville series, if it contains organic remains, may be supposed to afford species differing from those of the Huronian, and to form a sort of oasis in the desert of the early pre-Cambrian world. We find that the limestones of this age actually contain remains supposed to be of animal origin. They were first found in Canada, which contains the largest and best exposed area of these rocks in the world, and were brought under the notice of geologists by the late Sir William E. Logan, the first director of the Geological Survey of that country.

In anticipation of details to be given later, the story of this discovery and its announcement may here be given in brief

As early as 1858, Sir William Logan had begun to suspect that certain laminated bodies found in the Laurentian limestones of the Grenville series might be of organic origin. The points which struck him were these: They differed from any known laminated concretions; they resembled the "Stromatoporæ" or layer-corals of the lower Palæozoic rocks next in succession to the Laurentian and Huronian; the forms were similar in all the specimens, while the mineralizing substances were different; they were found only in the limestone, and specially in one of the three great beds known in the formation, the upper limestone of the Grenville system. He exhibited specimens, and mentioned these probabilities at the meeting of the American Association in 1859. In 1862 it was suggested to Logan that the microscopic structure of some of the best preserved examples should be studied, and slices were accordingly prepared and submitted to the writer for examination. They revealed in the calcareous laminæ of the specimens complicated systems of canals or tubes filled with mineral matter, which appeared to be similar to those that Carpenter had recognised in the thickened parts of the shells of modern Foraminifera. This clew being followed, large numbers of slices of the supposed fossils and of the containing limestone and of similar limestones from other parts of the world were examined.

The writer also visited the localities of "Eozoon," and studied its mode of occurrence in situ. The facts ascertained were communicated to the Geological Society of London, the name "Eozoon Canadense" being proposed for the species. Its description was accompanied by a paper on the geological conditions by Logan, and one on the chemical conditions by Sterry Hunt, while supplementary notes were added by the late Dr. Carpenter and Professor T. Rupert Jones. Thus launched on the scientific world, "Eozoon" at once became a fertile subject of discussion, and volumes of more or less controversial literature have appeared respecting it. It still has its friends and opponents, and this may long continue, as so few scientific men are sufficiently acquainted on the one hand with the possibilities and conditions of the preservation of fossils in crystalline rocks, and on the other hand with the structures of modern "Protozoa." Thus, few are in a position to form an independent judgment, and "Eozoon" has met with some scepticism on the part both of biological and mineralogical specialists.

To aid us in forming an opinion, it will be necessary to consider the oldest known strata of the earth's crust, and the evidence which they afford of the condition of the world when they were deposited. As preliminary to this, we may look at the following table of pre-Cambrian formations in Canada.

SUCCESSION OF PRE-CAMBRIAN ROCKS IN
CANADA, AS UNDERSTOOD UP TO 1896.

(In descending order.)

THE FOUNDATIONS OF THE CONTINENTS, AND
THEIR GENERAL TESTIMONY AS TO LIFE

IV

THE FOUNDATIONS OF THE CONTINENTS, AND
THEIR GENERAL TESTIMONY AS TO LIFE

T

THAT the reader may be enabled better to understand the relation of the old foundations or pillars of the earth to the beginning of life, and the preservation of the remains of the earliest animals, it may be well to reverse the method we have hitherto followed, and to present a theoretical or ideal historical sketch of the early history of the earth, beginning with that stage in which it may be supposed to have been a liquid mass, considerably larger than it is at present, and intensely heated, and surrounded by a vast vaporous envelope composed of all the substances capable of being resolved by its heat into a gaseous condition—a smooth and shining spheroid, invested with an enormous atmosphere.

In such a condition its denser materials, such as the heavier metals, would settle toward the centre, and the surface would consist of lighter material composed of the less dense and more oxidizable substances combined with oxygen, and similar in character and appearance to the slag which forms on the surface of some ores in the process of smelting. Of this slaggy material there might, however, be different layers more or less dense in proceeding from the interior to the surface. This molten surface would, of course, radiate heat into space; and as it would naturally consist of the least fusible matters, these would begin to form a solid crust. We may imagine this crust at first to be smooth and unbroken, though such a condition could scarcely exist for any length of time, as the hardened crust would certainly be disturbed by ascending currents from within, and by tidal movements without. Still, it might remain for ages as a spheroidal crust, presenting little difference of elevation or depression in comparison with its extent. When it became sufficiently thick and cool to allow water to lie on its surface, new changes would begin. The water so condensed would be charged with acid substances which would begin to corrode the rocky surface. Penetrating into crevices and flashing into steam as it reached the heated interior, it would blow up masses and fragments of stone, and would perhaps force out and cause to flow over the surface beds of molten material from below the crust, and differing somewhat from it in their composition. All this aqueous work would accelerate the cooling and thickening of the crust, and at length a universal or almost universal heated ocean would envelope the globe, and so far as its surface was concerned, the reign of water would replace that of fire. We may pause here to consider the probable nature of the earth's crust in this condition.

The substance most likely to predominate would be silica or quartz, one of the lighter and most infusible materials of the crust; but which, heated in contact with alumina, lime, potash, and other earths and alkalis, forms fusible slags, enamels and glasses. One of these, composed of silica, alumina, and potash, or soda, was long ago named by the German miners felspar, a name which it still retains, though now several distinct kinds of it are distinguished by different names. Another is a compound of silica with magnesia and lime, forming the mineral known as Amphibole or Hornblende, and by several other names, according to its colour and crystalline form. In many deep-seated rocks these minerals are formed together, and having crystallized out separately give a spotted and granular character to the mass. Naturally colourless, all these minerals, and especially the felspar and hornblende, are liable to be coloured with different oxides of iron, the felspar usually taking a reddish, and the hornblende a greenish or blackish hue. Now, if we examine a fragment of the oldest or fundamental gneiss or granite, we shall see glassy grains of quartz, reddish or white flat-surfaced crystals of felspar, and dark-coloured prisms of hornblende. When destitute of any arrangement in layers, the rock is granite; when arranged more or less in flakes or laminæ, it is gneiss, the structure of which may arise either from its having been formed in successive beds, or from its having been flattened or drawn out by pressure. These structures can be seen more or less distinctly in any ordinary coarse-grained granite, or with the lens or microscope in finer varieties.

The Lower Laurentian rocks of our section consist essentially of the materials above described, with a vast variety in the proportions and arrangements of the constituent minerals. There is, there-fore, nothing to prevent us from supposing that these rocks are really remains of the lower portions of the original crust which first formed on the surface of our cooling planet, though the details of their consolidation and the possible interactions of heat and heated water may admit of much discussion and difference of opinion.

But after the formation of a crust and its covering in whole or in part with heated water, other changes must occur, in order to fit the earth for the abode of life. These proceeded from the tensions set up by the contraction and expansion of the interior heated nucleus and the solid crust—a complicated and difficult question, when we consider its laws and their mode of operation, but which resulted in the folding and fracturing of the crust along long lines which are parts of great circles of the earth, running in N.E. and S.W. and N.W. and S.E. directions; and these ridges, which in the earliest Archæan period must have attained to great height and very rugged outlines, formed the first rudiments of our mountain chains and continents. Those constituting the Laurentian nucleus of North America—a very simply outlined continent—form a case in point ([Fig. 18]).

The elevation of these mountain ridges forced the waters to recede into the lower levels. As the old psalm of creation has it,—

"The mountains ascend,

the valleys descend into

the place Thou hast founded

for them,"

and so sea-basins and land were produced.

Milton merely paraphrases this when he says,—

"The mountains huge appear

Emergent, and their broad, bare backs upheave

Into the clouds; their tops ascend the sky.

So high as heaved the tumid hills, so low

Down sunk a hollow bottom wide and deep.

Capacious bed of waters."

Englishmen have been accused of taking their ideas of creation from Milton rather than from nature or the Bible. Milton had not the guidance of modern geology. His cosmology is entirely that of a close student of the Biblical narrative of creation. He is in many respects the best commentator on the early chapters of Genesis, because he had a very clear conception of the mind of the writer, and the power of expressing the ideas he derived from the old record. For the same reason he is the greatest bard of creation and primitive man, and surprisingly accurate and true to nature.

Fig. 18.—Map of Laurentian, North America.
Showing the protaxis or nucleus of the continent.

Then began the great processes of denudation and sedimentation to which we owe the succeeding rock formations. The rains descended on the mountain steeps, and washed the decaying rocks as sand, gravel and mud into the rivers and the sea. The sea itself raged against the coasts, and cut deeply into their softer parts; and all the detritus thus produced by atmospheric and marine denudation was spread out by the tides and currents in the bed of the ocean, and its gulfs and seas, forming the first aqueous deposits, while the original land must have been correspondingly reduced.

The sea might still be warm, and it held in solution or suspension somewhat different substances from those now present in it, and the land was at first a mere chaos of rocky crags and pinnacles. But so soon as the temperature of the waters fell somewhat below the boiling point, and as even a little soil formed in the valleys and hollows of the land, there was scope for life, provided that its germs could be introduced.

On a small scale there was something of this same kind in the sea and land of Java, after the great eruption of Krakatoa, in 1883. The bare and arid mountain left after the eruption, began, in the course of a year, to be occupied by low forms of vegetable life, gradually followed by others, and verdure was soon restored. The once thickly peopled sea-bottom, so prolific of life in these warm seas, but buried under many feet of volcanic ashes and stones, soon began to be re-peopled, and is now probably as populous as before. But in this case there were plenty of spores of lichens, mosses, and other humble plants to be wafted to the desolate cone, and multitudes of eggs and free-swimming germs of hundreds of kinds of marine animals to re-people the sea-bottom. Whence were such things to come from to occupy the old Archæan hills and sea-basins? and all our knowledge of nature gives us no answer to the question, except that a creative power must have intervened; but in what manner we know not. That this actually occurred, we can, however, be assured by the next succeeding geological formation. We have seen that the granitic and gneissic ridges could furnish pebbles, sand, and clay, and these once deposited in the sea-bottom could be hardened into conglomerate, sandstone and slate. But beside these we have in the next succeeding or Upper Laurentian formation rocks of a very different character. We have great beds of limestone and iron ore, and deposits, of carbon or coaly matter, now in the peculiar state of graphite or plumbago, and it is necessary for us to inquire how these could originate independently of life. In modern seas limestone is forming in coral reefs, in shell beds, and in oceanic chalky ooze composed of minute microscopic shells; but only in rare and exceptional instances is it formed in any other way; and when we interrogate the old limestones and marbles which form parts of the land, they give us evidence that they also are made up of calcareous skeletons of marine animals or fragments of these.

Fig. 19.—Distribution of Grenville Limestone in the district north of Papineauville, with section showing supposed arrangement of the beds.
Scale of Map 7 miles to one inch. See also Dr. Bonney's paper, Geol. Mag., July, 1895.
Dotted area: Limestone. Horizontal lines: Upper gneiss (fourth gneiss of Logan). Vertical lines: Lower gneiss (third gneiss of Logan). Diagonal lines: Overlying Cambrian and Cambro-Silurian (Ordovician). (See also [Fig. 19A].)

Now when we find in the Grenvillian series, the first oceanic group of beds known to us, great and widely extended limestones, thousands of feet in thickness, and rivalling in magnitude those of any succeeding period, we naturally infer that marine life was at work. No doubt the primitive sea contained more lime and magnesia than the present ocean holds in solution; but while this might locally favour the accumulation of inorganic limestones, it cannot account for so great and extensive deposits. On the other hand, a sea rich in lime would have afforded the greatest facilities for the growth of those marine plants which accumulate lime, and through these for the nutrition of animals forming calcareous shells or corals. Thus we have presumptive evidence that there must have been in the Upper Laurentian sea something corresponding to our coral reefs and shell-beds, whatever this something may have been.

These limestones, however, demand more particular notice ([Fig. 19]).

One of the beds measured by the officers of the Geological Survey is stated to be 1,500 feet in thickness, another is 1,250 feet thick, and a third 750 feet; making an aggregate of 3,500 feet.[14] These beds may be traced, with more or less interruption, for hundreds of miles. Whatever the origin of such limestones, it is plain that they indicate causes equal in extent, and comparable in power and duration, with those which have produced the greatest limestones of the later geological periods. Now, in later formations, limestone is usually an organic rock, accumulated by the slow gathering from the sea-water, or its plants, of calcareous matter, by corals, foraminifera, or shell-fish, and the deposition of their skeletons, either entire or in fragments on the sea-bottom. The most friable chalk and the most crystalline limestones have alike been formed in this way. We know of no reason why it should be different in the Laurentian period. When, therefore, we find great and conformable beds of limestone, such as those described by Sir William Logan in the Laurentian of Canada, we naturally imagine a quiet sea-bottom, in which multitudes of animals of humble organization were accumulating limestone in their hard parts, and depositing this in gradually increasing thickness from age to age. Any attempts to account otherwise for these thick and greatly extended beds, regularly interstratified with other deposits, have so far been failures, and have arisen either from a want of comprehension of the nature and magnitude of the appearances to be explained, or from the error of mistaking the true bedded limestones for veins of calcareous spar.

[14] Logan: "Geology of Canada," [p. 45].

Fig. 19A.—Attitude of Limestone at Côte St. Pierre (see Map, [p. 88]).
(a) Gneiss band in the Limestone, (b) Limestone with Eozoon. (c) Diorite and Gneiss.

Again, in the original molten world, it seems likely that most of the carbon present—at least, at the surface—was in the atmosphere in the gaseous form of carbon dioxide. This might be dissolved by the rain and other waters; but we know in the modern world no agency which can decompose this compound and reduce it to ordinary carbon or coal, except that of living plants, which are always carrying on this function to an enormous extent. We know that all our great beds of coal and peaty matter are composed of the remains of plants which took their carbon from the air and the waters in past times. We also know that this coaly vegetable matter may, under the influence of heat and pressure, when buried in the earth, be converted into anthracite and into graphite, and even into diamond. It is true that an eminent French chemist[15] has shown that graphite and hydrocarbons may be produced from some of the metallic compounds of carbon which may have been formed under intense heat in the interior of the earth, by the subsequent action of water on such compounds; but there is nothing to show that this can have occurred naturally, unless in very exceptional cases. Now in the Grenvillian system in Canada there is not only a vast quantity of carbon diffused through the limestones, and filling fissures in other rocks, into which it seems to have been originally introduced as liquid bitumen, but also in definite beds associated with earthy matter, and sometimes ten to twelve feet thick. The occurrence of this large amount of carbon warrants us in supposing that it represents a vast vegetable growth, either on the land or in the sea, or both.

[15] Henri Moissan, "Proceedings Royal Society," June, 1896,

In like manner, in later geological periods, beds of iron ore are generally accumulated as a consequence of the solvent action of acids produced by vegetable decay, as in the clay ironstones of the coal formation and the bog iron ores of later times. Thus the beds of magnetic iron occurring in the Upper Laurentian may be taken as evidences, not of vegetable accumulation, but of vegetable decay.

May not also the great quantity of calcium phosphate mined in the Grenville series in Canada, indicate, as similar accumulations do in later formations, the presence of organisms having skeletons of bone earth?

With reference to the carbon and iron ore of the Grenville series, I may quote the following from a paper published in the Journal of the Geological Society of London in 1870:—

"The quantity of graphite in the Upper Laurentian series is enormous. In a recent visit to the township of Buckingham, on the Ottawa River, I examined a band of limestone believed to be a continuation of that described by Sir W. E. Logan as the Green Lake Limestone. It was estimated to amount, with some thin interstratified bands of gneiss, to a thickness of 600 feet or more, and was found to be filled with disseminated crystals of graphite and veins of the mineral to such an extent as to constitute in some places one-fourth of the whole; and making every allowance for the poorer portions, this band cannot contain in all a less vertical thickness of pure graphite than from twenty to thirty feet. In the adjoining township of Lochaber Sir W. E. Logan notices a band from twenty-five to thirty feet thick, reticulated with graphite veins to such an extent as to be mined with profit for the mineral. At another place in the same district a bed of graphite from ten to twelve feet thick, and yielding twenty per cent, of the pure material, is worked. When it is considered that graphite occurs in similar abundance at several other horizons, in beds of limestone which have been ascertained by Sir W. E. Logan to have an aggregate thickness of 3,500 feet, it is scarcely an exaggeration to maintain that the quantity of carbon in the Laurentian is equal to that in similar areas of the Carboniferous system. It is also to be observed that an immense area in Canada appears to be occupied by these graphitic and Eozoon limestones, and that rich graphitic deposits exist in the continuation of this system in the State of New York; while in rocks believed to be of this age near St. John, New Brunswick, there is a very thick bed of graphitic limestone, and associated with it three regular beds of graphite, having an aggregate thickness of about five feet.[16]

[16] Matthew, in Quart. Journ. Geol. Soc., vol. xxi. p. 423. "Acadian Geology," p. 662.

"It may fairly be assumed that in the present world, and in those geological periods with whose organic remains we are more familiar than with those of the Laurentian, there is no other source of unoxidized carbon in rocks than that furnished by organic matter, and that this has obtained its carbon in all cases, in the first instance, from the deoxidation of carbonic acid by living plants. No other source of carbon can, I believe, be imagined in the Laurentian period. We may, however, suppose either that the graphitic matter of the Laurentian has been accumulated in beds like those of coal, or that it has consisted of diffused bituminous matter similar to that in more modern bituminous shales and bituminous and oil-bearing limestones. The beds of graphite near St. John, some of those in the gneiss at Ticonderoga in New York, and at Lochaber and Buckingham and elsewhere in Canada, are so pure and regular that one might fairly compare them with the graphitic coal of Rhode Island. These instances, however, are exceptional, and the greater part of the disseminated and vein graphite might rather be compared in its mode of occurrence to the bituminous matter in bituminous shales and limestones.

"We may compare the disseminated graphite to that which we find in those districts of Canada in which Silurian and Devonian bituminous shales and limestones have been metamorphosed and converted into graphitic rocks not dissimilar to those in the less altered portions of the Laurentian.[17] In like manner it seems probable that the numerous reticulating veins of graphite may have been formed by the segregation of bituminous matter into fissures and planes of least resistance, in the manner in which such veins occur in modern bituminous limestones and shales. Such bituminous veins occur in the Lower Carboniferous limestone and shale of Dorchester and Hillsborough, New Brunswick, with an arrangement very similar to that of the veins of graphite; and in the Quebec rocks of Point Levi, veins attaining to a thickness of more than a foot are filled with a coaly matter having a transverse columnar structure, and regarded by Logan and Hunt as an altered bitumen. These Palæozoic analogies would lead us to infer that the larger part of the Laurentian graphite falls under the second class of deposits above mentioned, and that, if of vegetable origin, the organic matter must have been thoroughly disintegrated and bituminized before it was changed into graphite. This would also give a probability that the vegetation implied was aquatic, or at least that it was accumulated under water.

[17] Granby, Melbourne, Owl's Head, etc., "Geology of Canada," 1863, p. 599.

"Dr. Hunt has, however, observed an indication of terrestrial vegetation, or at least of subaërial decay, in the great beds of Laurentian iron ore. These, if formed in the same manner as more modern deposits of this kind, would imply the reducing and solvent action of substances produced in the decay of plants. In this case such great ore beds as that of Hull, on the Ottawa, 70 feet thick, or that near Newborough, 200 feet thick,[18] must represent a corresponding quantity of vegetable matter which has totally disappeared. It may be added that similar demands on vegetable matter as a deoxidizing agent are made by the beds and veins of metallic sulphides of the Laurentian, though some of the latter are no doubt of later date than the Laurentian rocks themselves.

[18] "Geology of Canada," 1863.

"It would be very desirable to confirm such conclusions as those above deduced by the evidence of actual microscopic structure. It is to be observed, however, that when, in more modern sediments, algæ have been converted into bituminous matter, we cannot ordinarily obtain any structural evidence of the origin of such bitumen, and in the graphitic slates and limestones derived from the metamorphosis of such rocks no organic structure remains. It is true that, in certain bituminous shales and limestones of the Silurian system, shreds of organic tissue can sometimes be detected, and in some cases, as in the Lower Silurian limestone of the La Cloche mountains in Canada, the pores of brachiopodous shells and the cells of corals have been penetrated by black bituminous matter, forming what may be regarded as natural injections, sometimes of much beauty. In correspondence with this, while in some Laurentian graphitic rocks,—as, for instance, in the compact graphite of Clarendon,—the carbon presents a curdled appearance due to segregation, and precisely similar to that of the bitumen in more modern bituminous rocks, I can detect in the graphitic limestones occasional fibrous structures which may be remains of plants, and in some specimens vermicular lines, which I believe to be tubes of Eozoon penetrated by matter once bituminous, but now in the state of graphite.

"When Palæozoic land-plants have been converted into graphite, they sometimes perfectly retain their structure. Mineral charcoal, with structure, exists in the graphitic coal of Rhode Island. The fronds of ferns, with their minutest veins perfect, are preserved in the Devonian shales of St. John, in the state of graphite; and in the same formation there are trunks of Conifers (Dadoxylon ouangondianum) in which the material of the cell-walls has been converted into graphite, while their cavities have been filled with calcareous spar and quartz, the finest structures being preserved quite as well as in comparatively unaltered specimens from the coal-formation.[19] No structures so perfect have as yet been detected in the Laurentian, though in the largest of the three graphitic beds at St. John there appear to be fibrous structures which I believe may indicate the existence of land-plants. This graphite is composed of contorted and slicken-sided laminæ, much like those of some bituminous shales and coarse coals; and in these there are occasional small pyritous masses which show hollow carbonaceous fibres, in some cases presenting obscure indications of lateral pores. I regard these indications, however, as uncertain; and it is not as yet fully ascertained that these beds at St. John are on the same geological horizon with the Grenville series of Canada, though they certainly underlie the Cambrian series of the St. John or Acadian group, and are separated from it by beds having the character of the Huronian, and thus come, approximately at least, into the same geological position.

[19] "Acadian Geology," p. 535. In calcified specimens the structures remain in the graphite after decalcification by an acid.

"There is thus no absolute impossibility that distinct organic tissues may be found in the Laurentian graphite, if formed from land-plants, more especially if any plants existed at that time having true woody or vascular tissues; but it cannot with certainty be affirmed that such tissues have been found. It is possible, however, that in the Laurentian period the vegetation of the land may have consisted wholly of cellular plants, as, for example, mosses and lichens; and if so, there would be comparatively little hope of the distinct preservation of their forms or tissues, or of our being able to distinguish the remains of land-plants from those of Algæ. The only apparent plant of the Laurentian to which a name has been given, Archæophyton of Britton, from New Jersey, consists of ribbon-like strips, destitute of apparent structure, and which, if they are of vegetable origin, may have belonged to either of the leading divisions of the vegetable kingdom. I have found similar flat frond-like objects in the limestone of the Grenville series, at Lachute, in Canada.

"We may sum up these facts and considerations in the following statements:—First, that somewhat obscure traces of organic structure can be detected in the Laurentian graphite; secondly, that the general arrangement and microscopic structure of the substance corresponds with that of the carbonaceous and bituminous matters in marine formations of more modern date; thirdly, that if the Laurentian graphite has been derived from vegetable matter, it has only undergone a metamorphosis similar in kind to that which organic matter in metamorphosed sediment of later age has experienced; fourthly, that the association of the graphitic matter with organic limestone, beds of iron ore, and metallic sulphides, greatly strengthens the probability of its vegetable origin; fifthly, that when we consider the immense thickness and extent of the Eozoonal and graphitic limestones and iron ore deposits of the Laurentian, if we admit the organic origin of the limestone and graphite, we must be prepared to believe that the life of that early period, though it may have existed under low forms, was most copiously developed, and that it equalled, perhaps surpassed, in its results, in the way of geological accumulation, that of any subsequent period."

Figs. 20 and 21.—Bent and dislocated Quartzite, in contorted schists interstratified with Grenville Limestone, near Montebello.
The Quartzites have been broken and displaced, while the schists have been bent and twisted. In the immediate vicinity the same beds may be seen slightly inclined and undisturbed.

Let us take, in connection with all this, the fact that we are dealing with the deposits of the earliest ocean known to us—an ocean warm and abounding in the mineral matters suitable for the skeletons of humble animals, and fitted to nourish aquatic plants. The conditions were certainly favourable to an exuberant development of the lower forms of marine life; and in later times, when such conditions prevail, we generally find that life has been introduced to take advantage of them. The prudent farmer does not usually allow his best pasture to remain untenanted with flocks and herds, and the Great Husbandman of nature has, so far as we know, been similarly careful.

I add two sections showing the local disturbances of beds of quartzite and schist associated with the Grenville limestones ([Figs. 20 and 21, page 103]).

PROBABILITIES AS TO LAURENTIAN LIFE, AND
CONDITIONS OF ITS PRESERVATION

V

PROBABILITIES AS TO LAURENTIAN LIFE, AND
CONDITIONS OF ITS PRESERVATION

W

WE have seen that the mineral constitution of the Upper Laurentian affords evidence that in this age there were already land and water, and that the processes by which the land is being worn down, and its materials deposited on the sea-bottom, were in full operation; while the absence of any evidence of violent wave-action, and the presence of thick deposits of limestone, coaly matter, iron ore, and fine-grained beds of sediment, indicates a time of rest and quiescence. All these conditions were favourable to the presence of life, and we should expect to find in such a period some sign of its commencement.

But here we are met by a formidable difficulty. If the beds of the Grenville series were originally deposits in a quiet sea, they are, as now existing in the old Laurentian hills and valleys, very much changed from their original condition. They have, in short, experienced the changes known to geologists by the formidable word metamorphism, whereby they have lost the more obvious characters of ordinary aqueous deposits, and have assumed new and strange forms. Dr. Adams, of Montreal, has taken the pains to collect a number of chemical analyses of the gneisses and schists or crystalline slates of the Grenville series, and finds that, however unlike to more modern shales and clays, they have substantially the same chemical composition. Now if they were originally such shales and clays, it has happened to them that the ingredients of the clays have rearranged themselves in new forms and become crystalline. We are familiar in a small way with such changes when brick clay, over-heated in the kiln, becomes fused into slag or vitrified; and if such slag were allowed to cool very slowly, it would present different kinds of crystalline minerals. We actually see changes of this kind in the substance of bricks which have been long exposed to intense heat in the walls of furnaces. Now in the crust of the earth, very old rocks, buried under newer deposits, and exposed to the heat of the interior molten rocks, experience such changes on a great scale; and there is one kind of influence present in the bowels of the earth which we in our experiments cannot easily imitate or understand, namely, the action of superheated water prevented by pressure from escaping as steam, and permeating the whole substance of deposits, which are thus baked at a high temperature in presence of water, instead of being exposed to mere dry heat, as in our kilns and furnaces. The study of the partial changes which have passed on later sediments where in contact with volcanic masses once intensely heated, enables us to understand the greater and more extensive metamorphism of the oldest rocks. Thus a mere mud becomes glorified by metamorphic crystallization into a micaceous schist. We have taken ordinary clay as an example; but under the same processes sand has been converted into a compact quartzite, ordinary limestone into crystalline marble, clay-ironstone into magnetic iron ore, coal into graphite, and lavas or volcanic ashes into hard crystalline granites, gneisses, or pyroxene rocks or hornblendic schists, according to their original composition. There may exist portions of these old rocks which have been exempt from such alteration, but hitherto we have not been able to find them, and they are probably under the ocean bed, or deeply burled beneath later rocks, while the parts exposed are precisely those which have by their crumpling and pressure, and the influence of internal heat, become most hardened and altered, and have therefore best resisted denudation. We need not therefore be astonished if any organic remains originally present in such rocks should have perished, or should have been subjected to such changes of composition and form as to have altogether lost their original characters. The searcher for fossils in such rocks has to expect that these can have been preserved only under very rare and exceptional circumstances. We have now to consider what these circumstances are, and for simplicity may suppose that we are endeavouring to discover in a crystalline limestone the remains of animals having a skeleton of limestone, as is the case with most shell-fishes and corals, and with many Protozoa and marine worms. In regard to these, we have to consider what may happen to them when they are imbedded in calcareous marl or ooze, or the limestone which results from the hardening of such materials; and we have to bear in mind that such organisms usually consist of hard, stony walls or partitions, enclosing cavities originally filled with the soft parts of the animal which may be supposed to have disappeared by decay before or during the mineralization of its skeleton.

So long as the imbedding mass continues soft and incoherent, shells, corals, etc., can be recovered in a condition similar to that of recent specimens, except that they may have become bleached in colour and brittle in texture, owing to the removal of organic matter intimately associated with the lime, and that their cavities may have been filled with sand or silt washed into them, or with calcite or calcareous spar introduced in solution in water. But if the containing mass has become a hard stone, the material filling the interior of our shell or coral has experienced a similar change; and when we break open the stone, we may obtain the specimen, now hard, solid, and heavy, but still showing more or less of its outer surface and markings, and possibly to some extent also its internal structure when it is sliced and studied under the microscope. But if the whole mass has been metamorphosed, and has become crystalline, the contained fossil and its contents may have experienced a similar change, and may have so coalesced with the containing matrix that it is no longer separable from it. Even in this case, however, if the whole is reduced to a thin transparent slice and examined microscopically, some traces may be found of the external and internal limiting lines of the fossil, and even of its minute structures, which often cause it to present an appearance granular, cellular, or otherwise different from that of the enclosing matrix. It requires, however, both skill and care to detect organic remains in such circumstances, and they may often escape observation, except when, as in many old crystalline limestones, the fossils are darkened in whole or in part with coaly matter derived from the decay of their own organic substance. The crystalline Trenton limestone of Montreal, used there as a building stone, is an excellent example ([Fig. 22]).

Fig. 22.—Section of "Trenton Limestone" (magnified).
Showing its composition of fragments of calcareous fossils.

Fig. 23.—Diagram of different States of Fossilization of the Cell of a Tubulate Coral.
(a) Natural condition, (b) Cell filled with calcite. (c) Walls calcite, filling silica. (d) Walls silica, filling calcite. (e) Both walls and calcite silica. All these conditions are found in the fossil corals of the corniferous Limestone of Canada—Middle Permian.

It is otherwise, however, when the calcareous fossils have been filled or injected with some mineral matter different from the matrix, as, for example, silica or some silicate, oxide or sulphide of iron. In this case the texture, colour, or hardness of the filling appear different from those of the limestone, and may be seen in a fresh fracture or polished slice; or when the rock is weathered, the hard mineralizing substance may project from the surface of the specimens, or may be disclosed by treating the surface with a weak acid. The figures here given may suffice to show some of these conditions of mineralization in ordinary limestones, and the effects which they produce ([Fig. 23]).

The mineral matters which thus aid in preserving fossils are of various kinds, and the whole subject is a very curious one; but for the present we may content ourselves with two kinds of mineralization—that by silicates and that by magnesian limestone or dolomite.

From the bottom of modern seas the dredge often brings up multitudes of minute shells, especially those of the simple gelatinous Protozoa, known as Foraminifera, whose internal cavities and pores have been filled with a greenish mineral composed of silica, iron and potash, combined with water (or, chemically speaking, a hydrous silicate of iron and potassium), which is named glauconite from its bluish-green colour—a name which we shall do well to remember. In such compounds, bases of similar chemical properties often replace one another, so that various glauconites differ somewhat in composition, the iron being in part often replaced by alumina or magnesia, and the potash by soda. The combined water also differs somewhat in its percentage. When minute shells fossilized in this way are treated with an acid so as to remove the calcareous shell itself, the enclosed silicate remains as a beautiful cast or core, representing all the forms of the interior, and any pores that may have penetrated the walls, and also perfectly representing the soft gelatinous body of the animal which once tenanted the shells ([Fig. 24]). (See also [Fig. 25] at end of chapter.)

Fig. 24.—Cast of Cavities of Polystomella in Glauconite (magnified).
After a photograph from Dr. Carpenter, and mounted specimens from his collection.

When we examine oceanic sediments of older date, we find similar fillings in limestones, chalks, and sandstones of various ages, some of the latter containing glauconite so abundantly as to bear the name of green-sands, from their colour; and in these older examples we more frequently find alumina and magnesia occupying a large place in the mineralizing silicate. [Fig. 24A] gives two illustrations of this—one a crinoidal stem from the Silurian of New Brunswick, injected with a silicate of alumina, iron, magnesia and potash; the other a spiral shell from more ancient perhaps Cambrian rocks in Wales, filled with a silicate apparently more nearly related to serpentine. Further examples will be referred to in an appended note.

Fig. 24A.—(a) Joint of Crinoid injected with a Hydrous Silicate, Silurian, Pole Hill, New Brunswick. (× 25.)
(b) Spiral Shell injected with a Hydrous Silicate allied to Serpentine, near Llangwyllog, North Wales, (× 25.)

We may now consider shortly the relation of dolomite, or the mixed carbonates of lime and magnesia, to the preservation of fossils. The presence of dolomite or magnesian limestone in these beds does not affect the conclusion as to their probable organic origin. This form of limestone occurs abundantly in later formations, and is even forming in connection with coral deposits in the modern ocean.

Dana has shown this by his observations on the occurrence of dolomite in the elevated coral island of Matea in Polynesia,[20] under circumstances which show that it was formed in the lagoon of an ancient coral atoll, or ring-shaped island, while he finds that coral and coral sands of the same elevated reef contain very little magnesia. He concludes that the introduction of magnesia into the consolidating under-water coral sand or mud has apparently taken place—"(1) In sea-water at the ordinary temperature; and (2) without the agency of any other mineral water except that of the ocean"; but the sand and mud were those of a lagoon in which the saline matter was in process of concentration by evaporation under the solar heat. Klement has more recently taken up this fact in the way of experiment, and finds that, while in the case of ordinary calcite this action is slow and imperfect, with the aragonite which constitutes the calcareous framework of certain corals,[21] and at temperatures of 60° or over, it is very rapid and complete, producing a mixture of calcium and magnesium carbonates, from which a pure dolomite more or less mixed with calcite may subsequently result.[22]

[20] "Corals and Coral Islands," p. 356, etc.

[21] Aragonite, like ordinary limestone, is calcium carbonate, but its atoms seem to be differently arranged, so as to make it a less stable compound, and it has a different crystalline form. Some calcareous organisms are composed of aragonite, others of ordinary calcite.

[22]"Bulletin Geol. Soc. Belgium," vol. ix. (1895, p. 3). Also notice in Geol. Mag., July, 1895, p. 329.

I regard these observations as of the utmost importance in reference to the relations of dolomite with fossiliferous limestones, and especially with those of the Grenville series. The waters of the Laurentian ocean must have been much richer in salts of magnesium than those of the present seas, and the temperature was probably higher, so that chemical changes now proceeding in limited lagoons might have occurred over much larger areas. If at that time there were, as in later periods, calcareous organisms composed of aragonite, these may have been destroyed by conversion into dolomite, while others more resisting were preserved, just as a modern Polytrema or Balanus might remain, when a coral to which it might be attached would be dolomitized, or might even be removed altogether by sea-water containing carbonic acid. There is reason to believe that this last change sometimes takes place in the deeper parts of the ocean at present. This would account for the persistence of Eozoon and its fragments, when other organisms may have perished, and also for the frequent filling of the canals and tubuli with the magnesian carbonate.

The main point here, however, for our present purpose is that, when a calcareous shell or skeleton has been thus infiltrated with a silicate, it becomes imperishable, so that any amount of alteration of the containing limestone short of its absolute fusion would not suffice to destroy an organism once injected with silicious matter. Thus the occasional persistence of silicified fossils in highly metamorphosed limestones is in no respect contradictory to the general fact, that when not preserved by silicious infiltration, they have perished, and this more especially in the case of those whose skeletons are composed of aragonite.

Carrying these facts with us, the next question is, What manner of fossil remains should we expect to find in the Upper Laurentian rocks, supposing that any such are therein preserved? The answer to this question follows at once from the facts as to the succession of life noticed above. Only the marine invertebrates have been traced as far back as the oldest Cambrian, and only Worms, Sponges, and Protozoa into the Huronian. We should therefore have no expectation of finding remains of any vertebrate animals or of any of the land invertebrates; and even allowing for the more favourable conditions, as compared with the Huronian, evidenced by the great limestones and the abundant carbon, we could scarcely expect anything higher than some of the lower types of invertebrate life, such as Worms, Hydroids, Corals and Protozoa. We have next to inquire what forms, possibly organic, have actually been found, and what information we can derive from them as to the beginnings of life. Since, however, such discoveries as have been made have been the result of much labour and scientific skill brought to bear on these old rocks, and are connected with the reputations of several eminent men, now deceased, we may first refer shortly to the history of the discovery of supposed fossils in the Laurentian rocks of Canada.

Fig. 25.—Nature-print of an etched Specimen of Eozoon.
Showing the laminæ, a part of the natural margin, near which passes a diagonal calcite vein, and at the upper right-hand corner, fragmental material with casts of Archæospherinæ. The dark lines represent the chambers filled with serpentine, the white the calcite wall.

THE HISTORY OF A DISCOVERY

VI

THE HISTORY OF A DISCOVERY

W

WHEN Mr. Logan, afterwards Sir William Logan, entered on the Geological Survey of Canada, in 1840, he found that vast and little-explored regions in the northern part of that country were occupied with gneissic rocks, similar to the oldest gneisses of Scotland and Scandinavia, and to which the name Azoic had been given by Murchison, as rocks destitute of fossils, while they had been the "fundamental granite" or ur-gneiss of most European geologists. They were unquestionably below and more ancient than the oldest fossiliferous Cambrian rocks both in Europe and North America, and geologists had for the most part contented themselves with regarding them as primitive rocks, destitute of any geological interest, much as some United States geologists of the present day call them the "Archæan complex," a name which the late Prof Dana has well characterized as a "term of despair."

Logan was, however, a man not to be daunted by an unsolved problem, even though the facts for its solution must be sought in a wilderness known to few except adventurous trappers, hunters, and lumbermen; and he soon learned that this ancient gneissic formation contained other rocks beside gneiss, more especially thick and extensive limestones, and that its beds seemed to have a definite arrangement, and could be traced over great areas. He addressed himself, therefore, to the problem of unravelling the tangled "complex," and with a few hardy assistants, spent years in laboriously tracing its beds along river courses and over mountains, and in mapping, in a manner never previously attempted, its several members, designating at the same time the whole by the term "Laurentian," because it constituted the mass of the hills lying north of the St. Lawrence, called by old French geographers the Laurentides, and separating the St. Lawrence Valley and the region of the great lakes from Hudson's Bay and the Arctic Sea. In this manner he laid a foundation, which still remains unshaken, for the geology of the oldest rocks, and prepared the way for the discovery of the forms afterward named Eozoon Canadense. At the same time Dr. Sterry Hunt, the chemist of the Survey, was examining chemically the rocks and minerals collected, and all Sir William's assistants were instructed to search, more especially in the limestones, for anything bearing the aspect of fossils. On the other hand. Dr. Carpenter was independently pursuing his studies of the humbler inhabitants of the modern ocean, and of the manner in which the pores of their skeletons became infiltrated with mineral matter, and had kindly contributed specimens to the collections of the writer in Canada. The discovery of this most ancient fossil was thus not the chance picking up of a rare and curious specimen, but the result of several combined lines of laborious and skilful research.

The following notice of the persons and incidents connected with its discovery is taken from a previous publication of the writer, with only a little alteration in terms to suit it to the present date.

The first specimens of Eozoon ever procured, in so far as known, were collected at Burgess, in Ontario, by a veteran Canadian mineralogist. Dr. Wilson of Perth, and were sent to Sir William Logan as mineral specimens. Their chief interest at that time lay in the fact that certain laminæ of a dark green mineral present in the specimens were found, on analysis by Dr. Hunt, to be composed of a new hydrous silicate, allied to serpentine, and which he named loganite, but which seems to be a mixture of different silicates. The form of this mineral was not suspected to be of organic origin. Some years after, in 1858, other specimens, differently mineralized with the minerals serpentine and pyroxene, were found by Mr. J. McMullen, an explorer in the service of the Geological Survey, in the limestone of the Grand Calumet on the river Ottawa. These seem to have at once struck Sir W. E. Logan as resembling the Silurian fossils known as Stromatoporæ, or layer-corals, and at that time of quite uncertain nature, though supposed to be allied to some kinds of modern corals. He showed them to Mr. Billings, the palæontologist of the Survey, and to the writer, with this suggestion, confirming it with the sagacious consideration that inasmuch as the Ottawa and Burgess specimens were mineralized by different substances, yet were alike in form, there was little probability that they were merely mineral or concretionary. Mr. Billings was naturally unwilling to risk his reputation in affirming the organic nature of such specimens; and my own suggestion was that they should be sliced, and examined microscopically; and that if fossils, as they presented merely concentric laminæ and no cells, they would probably prove to be protozoa rather than corals. A few slices were accordingly made, but no definite structure could be detected. Nevertheless, Sir William Logan took some of the specimens to the meeting of the American Association at Springfield, in 1859, and exhibited them as possibly Laurentian fossils; but the announcement was evidently received with some incredulity. In 1862 they were exhibited by Sir William to some geological friends in London, but he remarks that "few seemed disposed to believe in their organic character, with the exception of my friend Professor Ramsay." In 1863 the General Report of the Geological Survey, summing up its work to that time, was published, under the name of the "Geology of Canada," and in this, at page 49, will be found two figures of one of the Calumet specimens, here reproduced, and which, though unaccompanied with any specific name or technical description, were referred to as probably Laurentian fossils (Figs. [26] and [27]).

Fig. 26.—Weathered Specimen of Eozoon from the Grand Calumet. (Collected by Mr. McMullen.)

Fig. 27.—Cross Section of the Specimen represented in [Fig. 26].
The dark parts are the laminæ of calcareous matter converging to the outer surface.

About this time Dr. Hunt happened to mention to me, in connection with a paper on the mineralization of fossils which he was preparing, that he proposed to notice the mode of preservation of certain fossil woods and other things with which I was familiar, and that he would show me the paper in proof, in order that he might have any suggestions that occurred to me. On reading it, I observed, among other things, that he alluded to the supposed Laurentian fossils, under the impression that the organic part was represented by the serpentine or loganite, and that the calcareous matter was the filling of the chambers. I took exception to this, stating that though in the slices before examined no structure was apparent, still my impression was that the calcareous matter was the fossil, and the serpentine or loganite the filling. He said: "In that case, would it not be well to re-examine the specimens, and to try to discover which view is correct?" He mentioned at the same time that Sir William had recently shown him some new and beautiful specimens collected by Mr. Lowe, one of the explorers on the staff of the Survey, from a third locality, at Grenville, on the Ottawa. It was supposed that these might throw further light on the subject; and accordingly Dr. Hunt suggested to Sir William to have additional slices of these new specimens made by Mr. Weston, of the Survey, whose skill as a preparer of these and other fossils has often done good service to science. A few days thereafter, some slices were sent to me, and were at once put under the microscope. I was delighted to find in one of the first specimens examined, which happened to be cut parallel to the laminæ, a beautiful group of tubuli penetrating one of the calcite layers. Here was evidence, not only that the calcite layers represented the true skeleton of the fossil, but also of its affinities with the Foraminifera, whose tubulated supplemental skeleton, as described and figured by Dr. Carpenter, and represented in specimens in my collection presented by him, was evidently of the same type with that preserved in the canals of these ancient fossils. [Fig. 28] is an accurate representation of the first seen group of canals penetrated by serpentine.

On showing the structures discovered to Sir William Logan, he entered into the matter with enthusiasm, and had a great number of slices and afterwards of decalcified specimens prepared, which were placed in my hands for examination.