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.
Fig. 28.—Group of Canals in the Supplemental Skeleton of Eozoon.
Taken from the specimen in which they were first recognised. (Magnified.)
Fig. 29.—Canals of Eozoon, from same specimen,
(Highly magnified.)
Feeling that the discovery was most important, but that it would be met with determined scepticism on the part both of geologists and biologists, I was not content with examining the typical specimens of Eozoon, but had slices prepared of
every variety of Laurentian limestone, of altered limestones from the Cambrian and Silurian, and of serpentine marbles of all the varieties furnished by our collections. These were examined with ordinary and polarized light, and with every variety of illumination. Dr. Hunt, on his part, undertook the chemical investigation of the various associated minerals. An extensive series of notes and camera tracings were made of all the appearances observed; and of some of the more important structures beautiful drawings were executed by the late Mr. H. S. Smith, the then palæontological draughtsman of the Survey. The result of the whole investigation was a firm conviction that the structure was organic and probably foraminiferal, and that it could be distinguished from any merely mineral or crystalline forms occurring in these or other limestones.
At this stage of the matter, and after exhibiting to Sir William all the characteristic appearances in comparison with such concretionary, dendritic, and crystalline structures as most resembled them, and also with the structure of recent and fossil Foraminifera, I suggested that the further prosecution of the matter should be handed over to Mr. Billings, as palæontologist of the Survey, and as our highest authority on the fossils of the older rocks.
Fig. 30.—Casts of Canals of Eozoon, in Serpentine.
Decalcified and highly magnified.
Fig. 31.—Group of finest Tubuli.
Highly magnified, from a micro-photograph.
I was engaged in other researches, and knew that no little labour must be devoted to the work and to its publication, and that some controversy might be expected. Mr. Billings, however, with his characteristic caution and modesty, declined. His hands, he said, were full of other work, and he had not specially studied the microscopic appearances of Foraminifera or of mineral substances. It was finally arranged that I should prepare a description of the fossil, which Sir William would take to London, along with Dr. Hunt's notes, the more important specimens, and lists of the structures observed in each. Sir William was to submit the manuscript and specimens to Dr. Carpenter, and also to Prof T. Rupert Jones, in the hope that these eminent authorities would confirm our conclusions, and bring forward new facts which I might have overlooked or been ignorant of Sir William saw both gentlemen, who gave their testimony in favour of the organic and foraminiferal character of the specimens; and Dr. Carpenter in particular gave much attention to the subject, and worked out the structure of the delicate tubulation of the surfaces of the laminæ or cell-walls, which I had not distinguished previously, through a curious accident as to specimens. Mr. Lowe had been sent back to the Ottawa to explore, and just before Sir William's departure had sent in some specimens from a new locality at Petite Nation, similar in general appearance to those from Grenville, which Sir William took with him unsliced to England. These showed in a perfect manner the tubuli of the primary cell-wall, which I had in vain tried to resolve in the Grenville specimens, and which I did not see until after they had been detected by Dr. Carpenter in London. Dr. Carpenter thus contributed in a very important manner to the perfecting of the investigations begun in Canada, and on him fell the greater part of their illustration and defence,[23] in so far as Great Britain is concerned.
[23] In papers by Dr. Carpenter, subsequently referred to. Prof. Jones published an able exposition of the facts in the Popular Science Monthly.
The immediate result was a composite paper in the Proceedings of the Geological Society, by Sir W. E. Logan, Dr. Carpenter, Dr. Hunt, and myself, in which the geology, palæontology, and mineralogy of Eozoon Canadense and its containing rocks were first given to the world.[24] It cannot be wondered at that when geologists and palæontologists were thus required to believe in the existence of organic remains in rocks regarded as altogether Azoic and hopelessly barren of fossils, and to carry back the dawn of life as far before those Cambrian rocks, which were supposed to contain its first traces, as these are before the middle period of the earth's life-history, some hesitation should be felt. Further, the accurate appreciation of the evidence for such a fossil as Eozoon required an amount of knowledge of minerals, of the more humble types of animals, and of the conditions of mineralization of organic remains, possessed by few even of professional geologists. Thus Eozoon has met with some negative scepticism and positive opposition—though the latter has been smaller in amount than might have been anticipated, when we consider the novel and startling character of the facts adduced. The most annoying element in the discussion has consisted in the liability of observers, only partially informed, to confound our specimens with things of very different character, from which we had taken pains to distinguish them.
[24] In Quarterly Journal of Geological Society, vol. xxii.; Proc. Royal Society, vol. xv.; Intellectual Observer, 1865; Annals and Magazine of Natural History, 1874; and other papers and notices.
"The united thickness," says Sir William Logan, "of these three great series, the Lower and Upper Laurentian and Huronian, may possibly far surpass that of all succeeding rocks, from the base of the Palæozoic to the present time. We are thus carried back to a period so far remote that the appearance of the so-called Primordial fauna may be considered a comparatively modern event."[25] So great a revolution of thought, and this based on one fossil, of a character little recognisable by geologists generally, might well tax the faith of a class of men usually regarded as somewhat faithless and sceptical. Yet this new extension of life has been very generally received, and has found its way into text-books and popular treatises. Its opponents have been under the necessity of inventing the most strange and incredible pseudomorphoses of mineral substances to account for the facts. As might have been expected, after the publication of the original paper, other facts developed themselves. Mr. Vennor found other and scarcely altered specimens closely allied to the Laurentian forms in the Hastings series of Tudor, probably of Huronian age. Gümbel recognised the organism in Laurentian rocks in Bavaria and elsewhere in Europe, and discovered a new species in the Huronian of Bavaria.[26] Eozoon was recognised in Laurentian limestones in Massachusetts[27] and New York, and there has been a rapid growth of new facts increasing our knowledge of Foraminifera and other humble animals in the succeeding Eozoic and Palæozoic rocks. Special interest attaches to the discovery by Mr. Vennor, and by Walcott and Matthew, to be mentioned in the sequel, and tending to bridge over the interval between the Laurentian fossil and those of the Lower Cambrian. Another fact, whose significance is not to be over-estimated, is the recognition both by Dr. Carpenter and myself of specimens in which the canals are occupied by dolomite or by calcite like that of the organism itself I have made several visits to the locality at Petite Nation originally discovered by Mr. Lowe, in company with Dr. Carpenter, Dr. Bonney,[28] and other skilled observers, and have very carefully studied all the facts with reference to the mode of occurrence of the forms in the beds, and their association with layers of fragmental Eozoon, and have found that these are strictly in accordance with the theory that these old Laurentian limestones are truly marine deposits, holding the remains of the sea animals of their time.
[25] Journal Geological Society, February, 1865.
[26] Ueber das Vorkommen von Eozoon, 1866.
[27] By Mr. Bicknell at Newbury, and Mr. Burbank at Chelmsford. The latter gentleman has since maintained that the limestones at the latter place are not true beds; but his own descriptions and figures lead to the belief that this is an error of observation on his part. The Eozoon in the Chelmsford specimens and in those of Warren, New York, is in small and rare fragments in serpentinous limestone.
[28] See an excellent account of one of these visits by Dr. Bonney, Geological Magazine, 1895.
Eozoon is not, however, the only witness to the great fact of Laurentian life, of which it is the most conspicuous exponent. In many of the Laurentian limestones, mixed with innumerable fragments of Eozoon, there are other fragments with traces of organic structure of a different character. There are also casts in silicious matter which seem to indicate smaller species of Foraminifera; and large laminated forms, apparently organic, yet distinct from Eozoon. Some of these must be noticed in the following pages.
Other discoveries also are foreshadowed here. The microscope may yet detect the true nature and affinities of some of the fragments associated with Eozoon. Less altered portions of the Laurentian rocks may be found, where even the vegetable matter may retain its organic forms, and where fossils may be recognised by their external outlines as well as by their internal structure. Thus the time may come when the rocks now called Primordial shall not be held to be so in any strict sense, and when swarming dynasties of Protozoa and other low forms of life may be known as inhabitants of oceans vastly ancient as compared with even the old Primordial seas. Who knows whether even the land of the Laurentian time may not have been clothed with plants, perhaps as much more strange and weird than those of the Devonian and Carboniferous, as those of the latter are when compared with modern forests?
THE DAWN OF LIFE