laborious than that of making the discoveries themselves. But it is of essential service to the cause of science. Sir Roderick has done it now for the fourth time, and has brought his book abreast of the advancing science of his day.

In an exploratory journey it is common to reckon progress not merely from the last halt, but from the original place of departure. So in that life-long journey into the unknown which the man of science pursues, it is well now and then amid the increasing wealth of his discoveries, to look back to the time when he set out, and to the spot from which he started. We thereby gain a more vivid idea of the progress he has made, as well as of the point to which in his onward march he has come.

Looking back over an interval of nearly forty years to the state of knowledge regarding the oldest rocks at that time, we see how one by one the geological landmarks which have now been in use so long, and the non-existence of which is scarcely conceivable, disappear as our survey recedes into the past, until we arrive at a period when this portion of geology was shrouded in the deepest darkness and confusion. The vast series of deposits which underlies the carboniferous rocks, and which is now arranged in distinct systems and formations, was then included under one group, to which the name of transition or grauwacke was given. Under this appellation were thrown together the rocks now known as Devonian, the various members of the Silurian system, and the thick mass of strata comprehended under the name Cambrian. In this country a general similarity of character pervades the rocks of these different divisions; they are hard, jointed, often cleaved and contorted; and in the infancy of the science they were naturally enough looked upon as varying members of one ancient formation. Fossil remains were indeed known to exist amongst these rocks. The third edition of the late Sir Henry de la Beche's 'Geological Manual,' published in 1833, enumerates 126 genera and 547 species as having up to that time been found in the 'Grauwacke group.' But no attempt had yet been made to use these organic remains as tests for the chronological subdivision of the rocks containing them, as had been so happily done for the secondary rocks of England. It was believed that the strata had been so broken and altered by subterranean movements during the long succession of geological periods, that little order could be drawn from them. They were known to contain the earliest traces of life upon the globe, but the record had been so sadly defaced and mutilated that no one had yet been able, or perhaps had ever deemed it possible, to piece the fragments together and gather a connected story from them. This, then, was the task to which

Sir

Sir Roderick Murchison set himself so far back as the year 1831. Guided by the advice of his friend, the late Dr. Buckland, he broke ground upon the banks of the Wye, and gradually during several years working his way among the strata which rise out from under the old red sandstone in Hereford, Radnor, and Shropshire, discovered the clue to the history of the oldest fossiliferous deposits. He found that instead of being hopelessly broken and obscure, these strata could be separated into distinct formations, each characterised by its own peculiar assemblage of organic remains, and that a gradual progression from lower to higher forms of life could be traced between the oldest and the newest rocks of the series. Thus he established a hitherto unknown group of formations, which he classed together under the name of the Silurian system.' The work which he published with that title contained a chapter in the world's history which up to that time had remained unwritten. Originally the name had reference merely to a comparatively small tract of England and Wales; but it was soon found to be of worldwide application. The succession of organic existence discovered in the most ancient fossiliferous rocks of this country was ascertained to be repeated in other and widely separated regions. Thus Sir Roderick in elucidating the geological structure of a limited part of Britain, in reality found the key to the order of succession among the rocks of a large portion of the surface of the globe, and the 'Silurian system,' instead of retaining merely a local significance, became at once a familiar term to the geologists of every country.

Thirty years have since passed away. Hundreds and thousands of observers have been at work all over the world, and though many new facts have been brought to light, and much detail added to the earlier researches of Murchison, the grand outlines first traced by him have been only the more firmly established. Some notion may be formed of the progress which has been made, from the fact that while in 1833 only 547 species of fossils had been obtained from all the rocks older than the carboniferous system, in the recent edition of 'Siluria' nearly 1300 species are enumerated from the British Silurian rocks alone. And if to these are added the species found in other parts of Europe and in America, where Silurian strata are largely developed, the number will be enormously increased. But besides these additions to the fauna of the system, the succession and arrangement of rocks of Silurian age have been laboriously traced over many thousands of square miles. In Scandinavia and Russia, and through central Europe to the shores of the Atlantic and the Mediterranean, these rocks have been correlated

with the original British types; throughout America a like identification has been made. And now, gathering up the fruits of all this research, Sir Roderick has issued a new and much enlarged edition of his treatise on these ancient formations.

'Siluria' forms in itself a sort of cyclopedia of palæozoic geology. It furnishes a large amount of information regarding the geological structure of the British Islands, and even of foreign countries; it gives copious details for comparing the older formations throughout Europe and America; it contains a storehouse of data from which the order of succession among the early races of marine invertebrates is made out. Nor among this crowded array of facts are there wanting topics provocative of interesting speculation. Sir Roderick himself halts now and then in his laborious grouping of details to point out their relation to more general questions, and there are many places which naturally suggest a similar task to the reader. The book is one which has established for itself a place in every geological library. It is therefore almost beyond the pale of periodical criticism. But the present edition, in the additions which it has received, offers an opportunity of reviewing one or two of the most generally interesting discoveries recently made in the geology of the older formations, and of noticing some of the topics which are at this moment the chief subjects of discussion among geologists.

Foremost among the new announcements is the story of the Eozoon Canadense, in other words, the account of a formation infinitely older than the Silurian, yet containing traces of lowly forms of organised beings. Until only a few years ago, it was believed by many geologists that life was first breathed upon the globe during the accumulation of those vast masses of sandstone, grit, and slate that underlie the lowest members of the Silurian system. Hundreds and thousands of feet of rock, piled bed above bed and representing a succession of ancient sea-bottoms, had been searched with care, but only a few rare and humble forms of life had been discovered. It was thence inferred that these barren rocks represented an early period of the earth's history when the waters of the ocean were correspondingly devoid of life, and that the growing numbers of the fossils found in the succeeding formations, showed how when living things at last appeared they obeyed the command to increase and multiply. And what helped to foster this belief was the mystery that hung over the beginning of these earliest geological records. In this country, at least, no base had been found to the Cambrian rocks which had yielded the most ancient organisms. It was not known on what they rested, whether they were the oldest strati

fied

fied rocks, or whether vestiges of still more ancient sea-floors might not lie buried deep beneath them.

But a series of investigations had been in progress in Canada which were destined to throw much light upon this subject, and, indeed, to open out a new and still older leaf of the earth's history. Charged with the conduct of the Geological Survey of the Canadian Provinces, Sir William Logan, with a quiet energy and perseverance which have happily overcome all the hindrances whereby at different times the very existence of his Survey was imperilled, has found a formation of great thickness lying below all those hitherto known. He has traced it over an extent of country equal in size to France, and it may reach much further. It consists of rocks of a highly crystalline charactersuch as gneiss, mica-schist, and quartzite-rocks which in the early days of geology would have been regarded as vestiges of the first crust of the planet as it cooled from a molten condition. Treating this formation, however, as he had dealt with the other stratified deposits of the province, in conjunction with his small but able staff of assistants, he mapped out its folds and contortions, following its different bands of rock from river to river; even through wild regions where the primitive state of the country has not yet been modified by the settler. The announcement of his discovery was received with no little interest in this country, and the interest increased when the further tidings came not only that the newly-detected formation was of vast thickness, and could be surveyed in detail, but that it actually contained two distinct divisions, the younger of which lay upon the previously upturned edges of the older. For this fresh fact furnished another proof, if any such addition had been needed, that Sir William had brought to light not a mere congeries of crystalline masses erupted from a heated interior, but a great stratified formation formed out of the waste of pre-existing rocks. That the one portion lay unconformably upon the other showed that the older strata-undoubtedly formed under the sea-had been elevated by subterranean action, and partly worn away again by the atmosphere and the waves before the newer strata, derived from this denudation, were laid down. Hutton had long ago said that geology revealed no traces of a beginning; and though here Sir William Logan has carried us inconceivably further back into the history of our planet, we are as far as ever from detecting any evidence of a truly primitive rock. We see traces of the same kinds of action as are still in operation around us-rocks being ground down into sediment, and the sediment carried into the sea, there to form new rocks, which in time are

raised up into land and worn away as before. But there was one feature of the Canadian discovery which inspired a hope that eventually we might be able not only to carry back in this way the history of existing geological causes, but to find that life appeared upon the globe long anterior to that dim, obscure Cambrian period, during some part of which it had been thought to have had its beginning. Among the old crystalline rocks of Canada-named Laurentian, from their development along the northern shores of the St. Lawrence-there lay some extensive beds of limestone. Now, though chemical or other forces had so mineralized and changed these rocks from their original character of marine sediment that their true stratified nature could hardly be recognised save on the large scale, and though able chemists maintained that the limestones were chemical and mineralogical segregations, having no connexion with organic action like the limestones of more recent formations, still the hope could not be thrown aside that some fortunate observer might chance to light upon traces of fossils in these, the oldest known calcareous beds in the world. Sir William Logan himself had looked long and anxiously, but without success. had indeed detected a suspicious object in the limestone which seemed to him to be organic, and to resemble some of the so-called corals of the Silurian series. But the specimen was too obscure for identification. At last he was able to submit to Dr. Dawson, of Montreal, another portion, in which that naturalist recognised the structure of a foraminifer. So important an announcement deserved all the confirmation which could be obtained for it. The specimens were accordingly placed in the hands of Dr. Carpenter, our highest authority on the microscopic structure of such organisms as the Canadian fossils were believed to be. By him the decision of Dr. Dawson was fully borne out, and the true organic nature of the substance confirmed. The fossil has been named the Eozoon Canadense, and up to the present time is the oldest relic of life which has been found upon the globe. It is believed to have grown in aggregated masses, forming reefs of rock, like the coral-reefs of our own day. Hence the thick masses of limestone in which it is found may be due in large measure to the secretive powers of these humble animals.

He

The Laurentian rocks must have been separated by a vast lapse of time from the next formation which succeeds them. For during that interval they had been changed from the state of sand, mud, and gravel, into gnarled crystalline gneiss, schist, and quartz-rock, and in that altered state had been anew exposed to denudation. It is beyond that immense gap that Sir William Vol. 125.-No. 249. Logan's