PUTNAM'S MONTHLY. A Magazine of Literature, Science, and Art. VOL. V.-MAY, 1855.-NO. XXIX. THE LAST WORD OF GEOLOGY.* ABOUT a year since we took occasion, in a brief article in this Magazine, to glance at the general principles on which modern Geology is founded, and to notice very cursorily the important work of Professor Hall, yet in progress under the patronage of the State of New York. The appearance of the two other standard books cited below, one containing the most thorough examination of a particular group of fossil relics ever made within a limited district, the other a general survey and resumé of the facts collected by geologists working in the older rocks over the whole hitherto explored area of our globe, forms a fair occasion for a second paper on a subject in which an intelligent interest is more widely felt every containing most of the known beds of coal. To these succeed the yet later series of strata which geologists have conventionally divided into the Permian, Triassic, Jurassic, Cretaceous, and Tertiary systems, each, wherever found, lying above its predecessors, and the contained fossils of each later formation showing an advance more and more towards that condition of things which, in the upper and newer Tertiary, merges into the historical period of Man, and connects itself with the present. Left, as we are, without trustworthy data by which to estimate, even approximatively, the duration of the periods during which these great piles of matter, with their organic contents, were formed in the old ocean beds, our geological chronology is but a rude one; and its periods, like the dynasties of old Egypt, may be imagined indefinitely longer or shorter; though there is no doubt of their real existence, and any reasonable restriction of their limits must leave on the mind the vague impression of enormous cycles. We can only speak of them indefinitely, as in human history we allude to the dark ages, to the period of Roman empire, the epoch of early Egyptian civilization, the centuries of Celtic or Pictish barbarism. The antiquary can refer the relics which he finds, generally to some such period, yet he often knows not, within many centuries, the lapse of time since their • Système Silurien de Boheme. Par J. BARRANDE. Vol. I. Trilobites. Prague, 1853.--Siluria. The History of the oldest known Rocks containing Organic Remains. By SIR RODERICK IMPEY MURCHISON. London, 1854.—Palæontology of New York. By JAMES HALL. Vols I. and II. Albany, 1847, 1852. VOL. V.-29 fabrication. The dates of some historical events seem to oscillate for a thousand or two thousand years, now appearing quite within the light of thirty centuries, now sinking back into the dim and indefinite shadows of the dawn of history, which prevent even a random estimate of the distance from which their ghostly outlines loom and flicker on our vision. Thus it is with geological periods. No one can say whether the epoch of the coal formation dates back one million of our years, or seven, or seventy millions. These epochs are like the distances of the stars, and all we know is that some are far more distant than others, and that the nearer, though infinitely remote, seem close at hand compared with those which lie on the limits of our perception. The reader may therefore assume any lapse of time which pleases him, since the old Silurian strata were laid down, particle by particle, by the primal ocean. We have only to say that there appears to be a bottom to the Great Cemetery, a geological ne plus ultra, below which no relics of organic life are found, at which the geologic record begins. The previous leaves of "the stone book" are blank, and these first decipherable inscriptions commence the chapter of the Silurian system. It is thus written on the successive layers of a series of slate, sandstone, shale, and limestone strata, piled to the thickness of from four thousand to twenty thousand feet, and its characters are the fragments of the living forms of its parent sea. Since its formation, it has been in many places covered by newer deposits so as to be buried far below our reach In many places the ocean still rests upon it. In many places where it has been raised above water and bared of more modern masses, it has been so baked and changed by the earth's internal heat, so doubled up and distorted by the crumpling of our globe's crust, or so worn away by the action of the elements, and swept seaward to form newer systems of strata, that it is only here and there that we find portions of it well preserved for our examination. In England and Wales it is sadly distorted and broken up, though distinctly traceable both in its stratification and its fossils; it is well seen in Scandinavia; and extensively developed in North Russia, though concealed by wide plains of alluvial earth; in France, Spain, and on the Rhine, it has been successfully traced and studied. Hitherto, however, its best exposures are in the northern United States, and in Bohemia.† *Efforts have been made to obtain some idea of the actual amount of time elapsed during the geological history. One means of calculation has been drawn from the belief that the plants of the coal formation must have required a temperature of 22° Reaumur. The mean temperature of the coal districts being now only 8 Reaumur, it is considered that the earth has lost 14° of heat by cooling since the carboniferous epoch. By such experiments as have been made in regard to the cooling of rock, and the radiation of heat, M. Unger has calculated that for the earth to lose 14° of Reaumur would require nine millions of years. M. Hibert reduces this to five millions. But supposing the whole earth once to have been in a melted state, the time which must have elapsed, in its cooling to its present condition, is fixed at the liberal allowance of three hundred and fifty millions of years. Another form of calculation occurs to us. Wherever strata are formed, it must be from the waste of existing land. Consequently, an average deposit of one foot of rock (supposing the sea and land to be equal in area) implies an average reduction in the hight of the continents of an equal amount. Thus if we know how fast the continents have been worn down, we can tell approximately how fast the sea has filled up. Now the Mississippi is estimated by Mr. Lyell to discharge annually 3700 millions of cubic feet of earthy matter, which is an average waste from its basin of about one million square miles. A little calculation shows that this amount of waste implies an annual reduction of the surface of this basin to the amount of about 1-7.534 of a foot, or one foot in about 7.500 years. At this rate, to form an average deposit of ten thousand feet of fossiliferous strata over the globe (which is, perhaps, a fair random estimate of its real thickness), would have required seventy-five millions of years, which would thus be the age of the lower Silurian strata. Other estimates of the discharge of solid matter by the Mississippi vary from that we have quoted. Some are one third less, which would give a slower rate of wear to the continent, and increase our seventy-five millions to one hundred. The highest estimate makes the sediment of the river seven times greater than that adopted above, and would reduce our seventy-five millions to only ten. On the other hand, the sediment of the river is only half the weight and solidity of ordinary rock, and it would require two cubic feet of it, when condensed, to form one of such as the old strata. Moreover, if the proportion of land to sea be estimated as it now is, only one to three, this supposition would require three feet of waste from the land to fill the sea one foot, and thus would extend our estimate of time threefold. Our figures therefore stand at 10, 20, 60, 75, or 100 millions of years for the age of the oldest trilobites and fossil shells; and if this calculation proves nothing else, it shows the vagueness of all attempts to reduce to our measures of time the vast but indefinite periods of geology. The appreciation which is now bestowed on our remarkable development of the older rocks, and the labors among them of American geologists. is fairly stated in an article on Sir R. Murchison's book in the London Quarterly Review for October last. It is understood to be from the pen of one of the first authorities, Prof. Edward Forbes, whose untimely death has lately disappointed so many hopes, and called forth so many tributes of regret in Europe and America. We extract a few sentences:- "North America inight almost be said to be the head quarters of Silurianism. A glance at the excel The traveler who turns aside from his forty-mile-an-hour race through New York, at Utica, to spend an afternoon at Trenton Falls, visits a spot where some of the most interesting layers of this old deposit are laid open to our view. The West Canada Creek has not only removed the beds of gravel and clay which usually conceal the rocks, but has worn a deep and preeipitous chasm through the hard strata, exposing their edges in all to the depth of two or three hundred feet. Some, seventy or eighty feet of this thickness lie between the head of the staircase and the black, foam-streaked pool below, every successive layer older than that above it, and each one formed by the gradual accumulation of many years. Past the fern-draped and moss-covered edges of these layers the visitor descends, step by step, lower and lower into the records of the past, until, reaching the broad, level platforms of rock which extend along the brink of the swift amber current, he can sit down, and, closely examining the water-worn black limestone, see in it the dead and petrified shells and corals and trilobites which lived in the old Silurian days. No pleasanter hours are within our remembrance than those spent on these rocky ledges, where the mind alternates from the mystical interest of the past to the fresh beauty of the present; where the monotonous roar of the torrent mingles with your reverie until it seems the murmur of the old Silurian ocean itself; until, raising your eyes, suddenly appear the gray precipice, the solemn hemlocks, and the white sheet of the cascade, and you are recalled to the living charms of a spot which is left with most regret after the longest familiarity. This is one locality of the Silurian strata, one point where the oldest tombs of the Great Cemetery lie open, and where its remains are abundant. Yet the visitor who expects to gather a large collection of fossils in a few hours or days will be disappointed. Here the shells and corals lie, not as on the coast of Cuba, where in half a day we may examine miles of beach, where at a glance the eye can sweep over many yards, and where the soft sand permits us to pick from it with the fingers whatever object may attract our attention. No. These relics are not so easy of collection. Those which, like the trilobites, were composed of many pieces, nine times out of ten before they were buried, decayed and fell into fragments. The shells and corals also suffered more or less from decomposition, some of the larger shells being almost unknown in an entire state. And then with what an iron gripe does the rock hold them-penetrating every pore and cavity, adhering to every roughness of the surface, enveloping closely every spine or projection. The collector is tantalized by the sight of so many a fossil which is beyond his hope, projecting from some obstinate pile of layers, of many ruined by the wear of the elements, and of those which he attempts to secure he sees the greater portion fall into fragments under his hammer. A day of hard labor enables him to break up only a few cubic feet of rock, and but a small proportion of its contents will be secured in any tolerable condition. When in addition to this difficulty in collecting, we remember that it is only in limited localities, quarries, cliffs, or ravines, miles asunder, that these old deposits are accessible to us; that probably not one square yard of an hundred thousand can be seen at all, we may wonder that so much has been accomplished in their examination, and that Mr. Hall has been able to recognize and describe three hundred different species of fossils from the lowest one-third of our Silurian strata. It is only by years of constant devotion to the pursuit, that so great a portion of these old-world relics have been recovered, and so much learned of lent map appended to Sir Charles Lyell's travels will show how vast are the regions there occupied, even superficially, by Silurian deposits. Exceedingly prolific in organic remains and varied in mineral character, these beds have furnished the subjects of some of the most excellent geological treatises that have appeared during the last ten years. They are too numerous to be cited. It certainly is one of the most striking features of the science of the United States, that geology has taken root there deeply, and has ourished, perhaps, beyond any of the sister sciences. The American geologists have gained a worldwide fame, and deservedly. Their works are text-books in Europe, and standard members of our scienthe libraries. A considerable number of these excellent monographs have been published at the cost of different States of the Union, whose local governments have thus shown an advanced and enlightened irit, and a just appreciation of the advantages that must accrue to their citizens through the timely development of the resources of the land. We have much yet to hope from the onward-striding pace of American geology." their nature and relationship to living forms. The results of such labors in remote portions of the globe are now being connected into one great system. The work of Sir R. Murchison gives a coup d'ail of the present state of knowledge of the Silurian rocks throughout the world, traced out and identified as they have been by the peculiar character of their fossil remains. The same families of shells, corals, crustaceans, and encrinites characterize them in all regions yet explored, and more especially do the trilobites mark and define these strata. It is true that these fossils vary considerably in remote districts, yet their general correspondence is well marked. As we find at the present day, that in comparing the living shells of the British and American coasts of the Atlantic, about one-third are identical on both shores, while of the remainder a large proportion are of analagous or corresponding forms, and but few are widely different; so among the fossils left by an earlier ocean in remote districts, we find some identical throughout, being species which lived in all parts of the ancient sea; many others more restricted in their extension, but represented beyond their own limits by very similar or related forms; others still, very peculiar and confined to narrow localities. Thus, when we find a large proportion of the fossils of one rock in America identical, or closely similar to those of another in Englandespecially if a similar correspondence is traceable between the succeeding or preceding also-we are warranted in concluding that these rocks are nearly cotemporary in date. Such a correspondence is evident between our Niagara limestone and shale and the Wenlock limestone and shale of England. The identity of many of their fossils proves that when these masses were forming at the ocean bottom, three thousand miles asunder, the same billows rolled and the same living forms inhabited them in the remote regions where are now the fertile plains of western New York and the green hills of Shropshire. We have not room to follow out this subject, but we have said enough to indicate the manner in which the cotemporary age of strata is traced in different countries and continents, and to show how we recognize the old Silurian formations, wherever portions of them remain accessible to our scrutiny. Thus it is, that, in North and South America, Europe, Asia, Australia and Africa, the stony records of the first period of organic life on our planet have been found, and, to a considerable degree, connected and identified with each other. We know, by such investigations, the comparative ages of continents. The Alps and Himalayas being made up of rocks not older than the Jurassic period, while Northern New York appears never to have been covered with newer deposits than the Silurian; we may know that the former have been raised during comparatively modern times, being geological parvenues, while our Adirondacks are of the very first families of mountains, a relic of the earliest dry land of the older world. Their heads have been kept above water from the most ancient period; the trilobites crawled round their subaqueous slopes, while the Trenton limestone was beginning to settle from the sea; and since then, they have seen the whole series formed, carboniferous, secondary, tertiary and all. No wonder that they are deeply furrowed and worn. Thousands of feet of their hard granite have been washed away by rain and storm, and Mount Tahawus is now but the mere stump, the remaining core or nucleus of the pile which once stood there, overlooking the primal ocean. Tennyson, in finally disposing of his sleeping beauty and her prince, recognizes the superior antiquity of this part of our planet: "And on her lover's arm she leant, This poetical use of a geological fact comes appropriately from an author, who, in his Princess, tells us of his heroine, how she one day "rode to take The dip of certain strata to the North," and saw, projecting from the sheer edge of the cliff, "The bones of some huge bulk that lived ani roared Before Man was He, too, not only ornaments the walls of his ideal hall with the customary ar mor and antlers, but spreads round its pavement, among the "Carved stones of the Abbey ruin in the park, Huge ammonites, and the first bones of Time." We subterranean philosophers owe a special debt of gratitude to Tennyson, who has introduced us to the best literary society, so that the hammer and basket may be borne even on the slopes of Parnassus. But we have not yet spoken of M. Barrande's book, which lies before us in its full bulk of nearly one thousand quarto pages, accompanied by fifty plates; all admirably printed and engraved at the ancient city of Prague. We have shown that it is only by the most energetic and persevering research that the relics of Siluria have been collected and illustrated. Mr. Hall's book is an instance of this, being the fruit of fifteen or twenty years' study under the patronage of an enlightened State. This book of M. Barrande's is another, the result of twenty years' exploration in Bohemia, under the patronage of an enlightened prince, the Comte de Chambord, formerly M. Barrande's pupil. Private purses are rarely deep enough to enable their owners to go far with such enterprises, and it is equally honorable to the patron and the explorer, when the union of means to scientific zeal and ability is thus made to subserve the noble object of the acquisition of knowledge, and its diffusion among men. M. Barrande's book is devoted entirely to the trilobites of Bohemia, other fossils being postponed to future volumes, and it certainly seems to be an exhaustion of the subject. The Silurian rocks of Bohemia (considering only the fossiliferous strata apart from the lower masses which are barren of organic remains) extend nearly N. E. and S. W., with a length of about fifty miles and a width of fifteen, the capital city of Prague lying within their northeastern limit. The strata are, in the lower part, slates and sandstones; in the upper portion, limestone prevails extensively. Volcanic agencies have mingled among the layers large masses of trap rock, and the strata are so tilted up from their originally level position as to form a sort of basin, the strata dipping towards the centre, at an angle of from 30° to 45°, sometimes as steep as 70°, and in some instances standing on edge, perpendicularly. In these features of small extent, isolated position, and steep inclination of the strata, the Bohemian Siluria contrasts strongly with ours. In New York, the rocks of equivalent age lie nearly horizontal, as when first deposited, and spread away in vast unbroken sheets, hundreds of miles within the limits of this State, and many hundreds beyond, through Ohio, Kentucky, Tennessee, Canada, traceable to the Mississippi on one side, and to the lonely island of Anticosti on the other. same fossils may be found in them through all this extent, and the strata cover each other in unmistakable succession, undisturbed by faults or uplifts. These features give the greatest value and trustworthiness to observations here made, rendering them free from the errors into which the student is often led in disturbed regions. The The Silurian basin of Bohemia has not these advantages, but they are compensated by the abundance of its fossils, especially its trilobites, which render it, in the words of M. Barrande, "a Silurian California." Its limited extent has enabled him to explore it most thoroughly. We quote his own account of the manner in which he has reaped his harvest. "We have devoted many years to the exploration of the surface of this field, in order to establish the extent of its fossiliferous portion. During this time, we have collected and noted everywherein quarries, in ravines, in all localities where the rocks are laid bare-all traces of organic remains which came under our observation. Having thus formed an opinion as to which strata and localities promised us a harvest of fossils, we organized, since 1840, a systematic exploration to make up for the insufficiency of our own arm and hammer. In different districts we successively established workmen, either singly or associated together, according to the difficulty of the task, to excavate the rocks and to open and explore quarries. These workmen, supplied with all necessary implements, and practically instructed by working for some time in our own company, soon acquired the skill necessary to distinguish, at first sight, any trace of the organic remains which were the object of our studies. We have often had occasion to admire the intel |