Page images
PDF
EPUB

clined, and exhibit marks of disturbance in every form of fracture and irregular position. Those of the second series, on the contrary, (the newer red sandstone, lias and volite,) are either perfectly level or inclined imperceptibly to the horizon: they seldom show traces of internal derangement, and they rest transversely on the truncated edges of the strata of the former series. That the inclined strata were formed originally in a nearly horizontal position is highly probable; for the order of their superposition is very regular. But the convulsions to which they owe their present fractures, curvature and elevation, must have been long subsequent to their formation; for all the members of the series are affected in the same manner. As these disturbances very rarelylle extend to the over-lying beds, the lapse of a considerable interval of time between the deposition of the two series is clearly indicated. In consequence of the total want of conformity between these, and the occasional absence of some of the overlying formations, any member of one series may in this district be in contact with any member of the other.

We regret that we cannot present to such of our readers as may not be familiar with the first principles of geology an intelligible analysis of this admirable memoir without extending the present Article to an unreasonable length. But even those who have never before directed their attention to this subject will readily perceive the advantages derivable from the knowledge of the superposition of a succession of formations once ascertained to be constant and regular. In the eastern part of England, where few formations, reckoning from the new red sandstone upwards, are ever wanting, costly trials have been often made to obtain coal; and in some instances the operations have commenced in very recent deposits. In the present state of geological science such futile attempts will scarcely be repeated. In the west of England trials have been frequently made to reach coal by shafts sunk through strata now known invariably to occupy an inferior alle position to the coal measures when both are present. Wherever

, in the map to which we have alluded, we find greywacke, transition limestone, mountain limestone, or old red sandstone, depicted as the superficial rock, it would be clearly absurd to sink for coal. As the coal measures are divisible into groups

of strata, preserving among themselves a regular order of succes• sion, and distinguishable by mineralogical character and organic remains, an attention to these points may often assist the judgment when the propriety of enlarging operations in mines already worked with profit is to be decided on. 'An extensive comparison moreover of the relations of the two series of formations enables the geologist to form an opinion of the probability of obtaining

[ocr errors]
[ocr errors]

400

coal

only of different genera, but of three distinct classes of former systems, all united and blended together in one single individual,

To enter at large into the consideration of other classes of organic remains, or to examine in detail those described in the present volume, would be inconsistent with our present limits and scope. In the illustration of these objects, lithography has been successfully employed. This art, so strongly recommended by its surior cheapness, may exert a favourable influence on the future progress of science, and particularly on natural history, which has always been retarded by the unavoidable expense of engraving. The plates descriptive of the osteological structure of the large Reptiles we have been mentioning deserve especial commendation, as do the figures of plants discovered by Mr. Mantell in the same strata with the Iguanodon, near Cuckfield in Susses. These remains consist partly of ferns, that numerous fossil genus, and partly of vegetables analogous to the genera Zamia and Cycas, now particularly characteristic of tropical regions. The plates of Orthoceræ* from the islands of Lake Huron are also admirably executed in lithography. These chambered univalve shells, so interesting to the conchologist from the peculiar structure of the siphuncle, are described in a paper by Dr. Bigsby on the geology of part of North America bordering on Lake Huron. No recent species of Orthocera hitherto discovered exceeds half an inch in length; the fossil species both in Europe and America frequently attain the length of many feet. The only multilocular univalve Testacea of large dimensions now existing are some species of Nautilus, and these are confined to tropical climates. The abundance therefore of Ammonites, Orthoceræ, and Nautili of great magnitude, in the strata of Europe and North America, is worthy of observation, as tending, in concurrence with other branches of organic remains, to confirm that striking deduction of geology, that the former temperature of the northern hemisphere was much higher than it is at present.

As the fossil species appear to be all, with very few exceptions, extinct, we reason only from analogy when we draw this conclusion, and we ought therefore to require a great accumulation of evidence, together with perfect harmony in the proofs. This question, concerning the former temperature of the globe, is extremely interesting, and it has so often been alluded to during our consideration of fossil animals and plants, that we shall lay before

* However great may be the expedience of a speedy reform in the nomenclature of natural history, we must not attempt it in this place. It may be as well, in compassion to the uninitiateri, to inform them that, when Lamarck writes Orthocera, he means Orthoceras, and that, tire language now spoken by conchologists, Orthoceræ stands for Orthocerata.

Our

our readers a concise view of the principal data on which the prevailing opinions of naturalists in regard to it are founded.

Remains of large herbivorous quadrupeds occur in the superficial gravel of Europe and North America, referable to genera now contined to warmer climates. Their number does not diminish as we proceed northwards, but, on the contrary, the greatest abundance has been found in Siberia, where the vegetation is now so scanty and buried for so long a time under the spow of a polar winter, that it is impossible to conceive how herds of elephants could ever have existed there, had the climate been always so severe as it is at present. Various oviparous quadrupeds, tortoises, turtles, crocodiles, and those gigantic Saurian animals, which engaged our attention in an earlier part of this essay, are distributed in profusion throughout the strata of every part of Europe, some even in the most recent formations above the chalk, and others in different parts of the series, down to the lias and the copper-slate of Thuringia inclusive. Nothing analogous to these classes of large reptiles exists at present in temperate latitudes.

Univalve shells are said to predominate in number over bivalves throughout the secondary strata in Europe, as at present in tropical seas.* To the occurrence of large chambered univalve shells, and the conclusions to which they point, we need not again refer. Corals and other zoophytes are found at present to increase in size, in variety of species, and rapidity of growth, as we approach the equator. They form large reefs in intertropical seas, where their comminuted fragments constitute a considerable portion of the beach, and are remarkable for their tendency to consolidate, with other loose materials, into rock. Such a state of things must be supposed to have existed when the colitic series and many other strata in Europe were deposited. But as we ascend towards the superior and more recent formations, which contain genera of shells more analogous to those now inhabiting our seas, fossil zoophytes become much rarer and inferior in size.

The above inferences are derived from so extensive a collection of facts, that the number of exceptions must be regarded as singularly small, and most of these are merely founded on analogy like the evidence on the other side. Remains of Cetaceous animals, for example, of a genus now exclusively tropical, have been discovered in a limestone in France, the calcaire grossière, with a species of another Cetaceous genus now peculiar to the frozen zone.t. A more remarkable exception occurs in the discovery of degree of moral advancement, and the comparative political power of our own and many other countries is thus shown to be connected with the former existence of a race of plants now extinct, which bore but a faint analogy to living species, and flourished at periods of immense antiquity, probably under a climate and in a state of the earth widely distinct from the present, the mind is elevated to an exalted conception of the magnificent extent of the whole system of nature, and of the wonderful relations subsisting between its remotest parts. The present disposition of the strata in the carboniferous series, and indeed in every other formation, is the best, if not the only conceivable, arrangement, by which each might be made to rise in succession to the surface, and present in its turn a variety of useful minerals or of soils adapted for different agricultural purposes. Had the strata been permitted to remain horizontal, they would have invested the nucleus of the earth, as Dr. Buckland has justly observed, in concentric coats, and the inferior must have been buried for ever beneath the highest.'* Now it scarcely admits of a doubt that the agents employed in effecting this most perfect and systematic arrangement have been earthquakes, operating with different degrees of violence and at various intervals of time during a lapse of ages. The order that now reigns has resulted therefore from causes, which have generally been considered as capable only of defacing and devastating the earth's surface, but which we thus find strong grounds for suspecting were, in the primeval state of the globe, and perhaps still are, instrumental in its perpetual renovation. The effects of these subterranean forces prove that they are governed by general laws, and that these laws have been conceived by consummate wisdom and forethought. Their consequences were formerly enumerated amongst the signs of anarchy and misrule, whence the Epicurean hypothesis originated that the earth was first formed, and has been since maintained, by Chance; and in later times they have been appealed to as the visible manifestations of God's wrath and of a penal dispensation.

* Defrance, Tab. des Corps Org. Foss. 51. 125. + Cuv. Discours sur les Rer. p. 313.

bones

After the unexpected discoveries, for which we may already thank the Science of Geology, it can no longer be matter of surprize, that we remain in ignorance of the ends answered by many of the operations of nature and of her living works, in whose form and structure such infinite variety, contrivance and beauty are displayed. The zoophytes and testacea, whose exuviæ are entombed by millions in stratified rocks, contribute to our wants and enjoyments perhaps in a far greater degree than the analogous races that now hill the great deep with life. The fossil species have

Inaugural Lecture, p. 11. Oxford. 1819.

not

[ocr errors]

solution ; for we are not so warmly interested in favour of any theory, as to wish, with King Henry,

that one might read the book of fate
And see the revolution of the times
Make mountains level, and the continent,
Weary of solid firmness, melt itself

Into the sea.' But in the present state of our knowledge, it appears premature to assume that existing agents could not, in the lapse of ages, produce such effects as fall principally under the examination of the geologist. It is an assumption, moreover, directly calculated to repress the ardour of inquiry, by destroying all hope of interpreting what is obscure in the past by an accurate investigation of the present phenomena of nature.

Those naturalists who have prosecuted with the greatest success the study of fossil remains concur in opinion that the earth during the deposition of the secondary strata was not in a state of chaotic confusion. There are proofs of occasional convulsions, but there are also proofs of intervening periods of order and tranquillity. The notion of a continually decreasing energy in nature's power to modify and disturb the earth's surface first originated in the observation that strata of the highest antiquity have suffered the greatest and most general derangement. But such must be the necessary effect of the uniform action of the same cause throughout a long succession of ages; and the frequent unconformability of strata clearly shows that disturbances have taken place at many and at different periods. There would perhaps have been some weight in the argument if the derangement of recent deposits were not merely of more partial occurrence, but invariably on a scale of inferior violence. But the fact is far otherwise. We find the chalk in Ireland extensively intermixed with trap, and in Hampshire thrown together with more recent formations into a vertical position. · Beds of the purbeck series in Dorsetshire, and of the plastic clay in the Isle of Wight, are contorted in the same manner as primary clay slate. In no part of Europe are effects of disturbance displayed on so stupendous a scale as in the Alps. Yet the date of this convulsion is, geologically speaking, extremely modern, for marine strata as recent as the green sand, chalk, and even some tertiary formations are discovered in this chain at an elevation of more than ten thousand feet above the level of the sea. Professor Buckland has remarked that these Alpine tertiary deposits are contemporaneous fragments of the more extensive strata of the adjacent low countries.* Since then the disturbing

* On the Formation of Valleys by Elevation. Geol. Trans. vol. ii. 2d ser. p. 127.

force

« PreviousContinue »