Some Salient Points in the Science of the Earth

by Sir John William Dawson

In studying the fossil plants of the Carboniferous, so abundant in the fine exposures of the coal formation in Nova Scotia, two defects struck me painfully. One was the fragmentary and imperfect state of the specimens procurable. Another was the question, What preceded these plants in the older rocks? The first of these was to be met only by thorough exploration. When a fragment of a plant was disclosed it was necessary to inquire if more existed in the same bed, and to dig, or blast away or break up the rock, until some remaining portions were disclosed. In this way it has been possible to obtain entire specimens of many trees of the Carboniferous; and to such an extent has the laborious and somewhat costly process been effectual, that more species of carboniferous trees are probably known in their entire forms from the Coal formations of Nova Scotia than from any other part of the world. I have been amused to find that so little are experiences of this kind known to some of my confrères abroad, that they are disposed to look with scepticism on the information obtained by this laborious but certain process, and to suppose that they are being presented with imaginary "restorations." I think it right here to copy a remark of a German botanist, who has felt himself called to criticise my work: "Dawson's description of the genus (Psilophyton) rests chiefly on the impression made on him in his repeated researches," etc. "He puts us off with an account of the general idea which he has drawn from the study of them." This is the remark of a closet naturalist, with reference to the kind of work above referred to, which, of course, cannot be represented in its entirety in figures or hand specimens.[16]

[16] Solms-Laubach, "Fossil Botany." A pretentious book, which should not have been translated into English without thorough revision and correction.

As to the precursors of the Carboniferous flora, in default of information already acquired, I proceeded to question the Erian or Devonian rocks of Canada, in which Sir William Logan had already found remains of plants which had not, however, been studied or described. Laboriously coasting along the cliffs of Gaspé and the Baie des Chaleurs, digging into the sandstones of Eastern Maine, and studying the plants collected by the New York Survey, I began to find that there was a rich Devonian flora, and that, like that of the Carboniferous, it presented different stages from the base to the summit of the formation. But here a great advance was made in a somewhat unexpected way. My then young friends, the late Prof. Hartt and Mr. Matthew, of St. John, had found a few remains of plants in the Devonian, or at least pre-Carboniferous beds of St. John, which were placed in my hands for description. They were so novel and curious that inquiry was stimulated, and these gentlemen, with some friends of similar tastes, explored the shales exposed in the reefs near St. John, and when they found the more productive beds, broke them up by actual quarrying operations in such a way that they soon obtained the richest Devonian plant collections ever known. I think I may truly say that these young and enthusiastic explorers worked the St. John plant-beds in a manner previously unexampled in the world. Their researches were not only thus rewarded, but incidentally they discovered the first known Devonian insects, which could not have been found by a less painstaking process, and one of them discovered what I believe to be the oldest known land shell. Still more, their studies led to the separation from the Devonian beds of the Underlying Cambrian slates, previously confounded with them; and this, followed up by the able and earnest work of Mr. Matthew, has carried back our knowledge of the older rocks in Canada several stages, or as far as the earliest Cambrian previously known in Europe, but not before fully recognised in America, and has discovered in these old rocks the precursors of many forms of life not previously traced so far back.

The moral of these statements of fact is that the imperfections of the record will yield only to patient and painstaking work, and that much is in the power of local amateurs. I would enforce this last statement by a reference to a little research, in which I have happened to take part at a summer resort on the Lower St. Lawrence, at which I have from time to time spent a few restful vacation weeks. Little Metis is on the Quebec Group of Sir William Logan, that peculiar local representative of the lower part of the Cambro-Silurian and Upper Cambrian formations which stretches along the south side of the St. Lawrence all the way from Quebec to Cape Rosier, near Gaspé, a distance of five hundred miles. This great series of rocks is a jumble of deposits belonging at that early time to the marginal area of what is now the American continent, and indicating the action not merely of ordinary causes of aqueous deposit, but of violent volcanic ejections, accompanied perhaps by earthquake waves, and not improbably by the action of heavy coast ice. The result is that mud rocks now in the form of black, grey, and red shales and slates alternate with thick and irregular beds of hard sandstone, sometimes so coarse that it resembles the angular débris of the first treatment of quartz in a crusher. With these sandstones are thick and still more irregular conglomerates formed of pebbles and boulders of all sizes, up to several feet in diameter, some of which are of older limestones containing Cambrian fossils, while others are of quartzite or of igneous or volcanic rocks.

The whole formation, as presented at Metis, is of the most unpromising character as regards fossils, and after visiting the place for ten years, and taking many long walks along the shore and into the interior, and scrutinising every exposure, I had found nothing more interesting than a few fragments of graptolites, little zoophytes, ancient representatives of our sea mosses, and which are quite characteristic of several portions of the Quebec Group. With these were some marks of fucoids and tracks or burrows of worms. The explorers of the Geological Survey had been equally unsuccessful.

Quite accidentally a new light broke upon these unpromising rocks. My friend, Dr. Harrington, strolling one day on the shore, sat down to rest on a stone, and picked up a piece of black slate lying at his feet. He noticed on it some faintly traced lines which seemed peculiar. He put it in his pocket and showed it to me. On examination with a lens it proved to have on it a few spicules of a hexactinellid sponge—little crosses forming a sort of mesh or lattice-work similar to that which Salter had many years before found in the Cambrian rocks of Wales, and had named Protospongia—the first sponge. The discovery seemed worth following up, and we took an early opportunity of proceeding to the place, where, after some search, we succeeded in tracing the loose pieces to a ledge of shale on the beach, where there was a little band, only about an inch thick, stored with remains of sponges, a small bivalve shell and a slender branching seaweed. This was one small layer in reefs of slate more than one hundred feet thick. We subsequently found two other thin layers, but less productive. Tools and workmen were procured, and we proceeded to quarry in the reef, taking out at low tide as large slabs as possible of the most productive layer, and carefully splitting these up. The results, as published in the Transactions of the Royal Society of Canada,[17] show more than twelve species of siliceous sponges belonging to six genera, besides fragments indicating other species, and all of these living at one time on a very limited space of what is practically a single surface of muddy sea-bottom.[18] The specimens show the parts of these ancient sponges much more perfectly than they were previously known, and indeed, enable many of them to be perfectly restored. They for the first time connect the modern siliceous sponges of the deep sea with those that flourished on the old sea-bottom of the early Cambro-Silurian, and thus bridge over a great, gap in the history of this low form of life, showing that the principles of construction embodied in the remarkable and beautiful siliceous sponges, like Euplectella, the "Venus flower-basket," now dredged from the deep sea, were already perfectly carried out in this far-back beginning of life. This little discovery further indicates that portions of the older Palæozoic sea-bottoms were as well stored with a varied sponge life as those of any part of the modern ocean. I figure[19] a number of species, remains of all of which may be gathered from a few yards of a single surface at Little Metis. The multitude of interesting details embodied in all this it is impossible to enter into here, but may be judged of from the forms reproduced. These examples tend to show that the imperfection of the record may not depend on the record itself, but on the incompleteness of our work. We must make large allowance for imperfect collecting, and especially for the too prevalent habit of remaining content with few and incomplete specimens, and of grudging the time and labour necessary to explore thoroughly the contents of special beds, and to work out all the parts of forms found more or less in fragments.

[17] Additional collections made in 1892 show two or three additional species, one of them the type of a new and remarkable genus.

[18] 1889, section iv. p. 39.

[19] Frontispiece to chapter.

The point of all this at present is that patient work is needed to fill up the breaks in our record. A collector passing along the shore at Metis might have picked up a fragment of a fossil sponge, and recorded it as a fossil, or possibly described the fragment. This fact alone would have been valuable, but to make it bear its full fruit it was necessary to trace the fragment to its source, and then to spend time and labour in extracting from the stubborn rock the story it had to tell. Instances of this kind crowd on my memory as coming within my own experience and observation. It is hopeful to think that the record is daily becoming less imperfect; it is stimulating to know that so much is only waiting for investigation. The history never can be absolutely complete. Practically, to us it is infinite. Yet every series of facts known may be complete in itself for certain purposes, however many gaps there may be in the story. Even if we cannot find a continuous series between the snails of the Coal formation or the sponges of the Quebec Group and their successors to-day, we can at least see that they are identical in plan and structure, and can note the differences of detail which fitted them for their places in the ancient or the modern world. Nor need we be too discontented if the order of succession, such as it is, does not exactly square with some theories we may have formed. Perhaps it may in the end lead us to greater and better truths.