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of the materials which have been worn down and washed away from the mountains and bigh land, and afterwards deposited either in vallies far above the level of the sea, or on the banks of rivers and along the coasts of estuaries. The stony masses which this formation contains exhibit the most satisfactory marks of having been rolled and agitated in water; and the rich mineral stones which usually characterize the alluvial depositions of mountainvallies bear testiinony to the same origin. The fifth and last formation of Werner is the volcanic, including rocks both of true and pseudo-volcanic production, which, of course, are very local and partial in their occurrence and require no explanation.

The great merit of the Wernerian gegnosy, as it strikes us, is that it hardly seems to involve an hypothesis, as far at least as regards its leading principles. It is obvious from the nature and constitution of the mineral substances which compose the crust of the earth, that they must have been formed in a fuid state; and as fluidity must proceed either from fusion or from solution, the enquiry is narrowed to the consideration of these two causes. Now, passing over every other objection, it may be asserted in the most positive manner that it is impossible the stratified rocks could have been cousolidated by fire, because they contain, as we have already mentioned, organized bodies in an entire and perfect state; which must have been completely destroyed by such a degree of heat as would be necessary to fuse basalt. Besides, in the series of strata which make up the floetz, formation, we have coal and clay under the most stubborn and refractory rocks, só, according to the Huttonian hypothesis, we have to encounter the monstrous imagination, that the central fire melted hornblende, felspar, and agate, through a stralum of coal which it did not char, and through a bed of clay which it failed to indurate. Water therefore must be regarded as the sole cause of fluidity, and the chrystallized forın of the primitive or oldest rocks lends the strongest confirnaation to this opinion. It is an opinion, too, which corresponds with our earliest notions on this subject, and with the highest authority which can be referred to on matters of science. The only conception we can form of chaos is that of a mass of dark and troubled water, in which were contained, in a state of solution, the materials of which the outer coat of the earth is formed, and from which they were successively precipi. tated according to laws impressed upon them by the Almighty Creator. Nor let it be imagined that the period of time wlich must have elapsed before the third formation, being chielly mechanical, could be deposited, conveys any thing incompatible with the Mosaical history of the creation. It is only necessary to call to mine that Moses does not profess to give any account of chaos, and that it is not until the earth is nearly fitted to become

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the habitation of men that the sacred historian enters into particulars. Besides, the object of the brief statement with which the book of Genesis commences, was evidently not to teach a system of astronomy or any other branch of natúral science, but to impress upon the minds of the Israelites that God is the Creator of the world and of every thing contained in it; and we perfectly agree with Professor Kidd in thinking, that from such slight materials to attempt to explain the details of geological phenomena, or to limit the progress of knowledge by the literal interpretation of so brief and mysterious a history, are equally unreasonable. Were it necessary, however, to point out how scriptural truth is confirmed by the deductions of science, and even of geological science, we would mention the accumulated evidence which has been lately brought forward to prove, that the

of the human race; and the origin of the various arts and institutions which characterize man, are not more ancient than the Bible teaches. But to return to the subó ject in hand, we have no hesitation to describe the Wernerian theory as a system of general principles, more closely connected with facts, and explaining appearances much more satisfactorily than any other theory not strictly demonstrable, • The remark naturally recalls to mind the title of the Essay under our consideration, which respects “ the important evidence in support of a theory of the earth, deducible either from its general structure, or from the changes produced on its surface by the operation of existing causes."- Dr. Kidd - seems willing to avoid ranging himself under any particular, leader on the subject of geognosy, but we can discover that although he is very polite and good-natured towards Dr. Hutton and Professor Playfair, he is not quite a decided Anti-Wernerian. His book, indeed, is chiefly occupied with remarks and objections which apply exclusively to the views of Werner; but we can perceive that his forbearance in another quarter, seems rather to imply neglect than coincidence of opinion. Nor do the objections of Professor Kidd direct themselves against the essential doctrines of the Wernerian school, but rather against some of their technicalities and nomenclature. He cannot see, for exaraple, that the primitive rocks differ so much from those of the transition class as to justify the language in which they are described. He readily admits that the crystalline strata must trave been precipitated from soine medium containing their elementary parts in solution, and that, from granite to the red såndstone, all the rocks of the Werverian classitication are in some measure connected. But the difficulty with our author is, that the particular series and order of succession detailed in books, do not always hold in nature, that there are many interruptious

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and omissions, and that the rocks which are described as primitive are frequently found mixed with those of the second order. His objections, in short, do not reach the great question of the igneous or aqueous origin of mineral bodies, but solely respect certain minor points in the detail of classification.

* In reviewing,” says he, “ the history of the strata described in the ten preceding chapters it seems evident, to me at least, that their apparently arbitrary intermixture and general character is such as to preclude the possibility' of framing any rational hypothesis as to, their origin: and certainly there is no natural process in existence, capable of producing any of the commonest phenomena by which they are particularly characterized. Where, for instance, do we now see the formation of granite, or syenite, or porphyry, &c. ? where do we see the production of metallic veins, or of beds of rock salt, or even of genuine coal? On the truth of these posic

, tions I need not insist, since they are not likely to be disputed by even the most cursory observer: but as I may possibly be thought to have confounded the true arrangement of many

of the strata above described, I beg leave to offer a few remarks on that point.

“ In the preceding chapters I have attempted to shew, that the frequent alternations and mutual transitions, observable in the strata below the rock marl, are such as effectually to prevent a distinct classification of them: and I believe that even the rock marl not only appears under the varying form of mere clay, and fine and coarse grained gritstone, but that it sometimes assumes the character of a more or less perfectly defined porphyry and amyge

and even insensibly passes into any of the rocks from granite downwards, and alternates with many of them. But in saying this I do not mean to advance the indolent and unphiloso phical proposition, that, because any rock may insensibly be traced into almost any other, (a fact however which those who have seen most will be most ready to allow,) there is therefore no difference between them: nor do I deny that this change of character appears to be connected with some law, which in a general point of view has assigned its place to each series of rocks : so that in a geographical distribution, allowance being made for partial devia. tions, you pass from granite, mixed with hornblende rocks of va rious descriptions, upon that mixed class of slates and gritstones so very generally found contiguous to a granite district; and among the last mentioned you find interspersed the mountain lime and coal series; the whole being bounded by the rock marl formation, with its accompanying rock salt and gypsum. All that I maintain is this, that since the succession of the formations above the rock marl is usually to be traced with ease, and can be satisfactorily demonstrated to an indifferent spectator, the same succession in the formations below the rock marl ought also by analogy, if it exist, to be visible and demonstrable; and if not thus demonstra

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ble, it is in some degree probable, that there is no such succession. But if in addition to this it can be shewn, which is I believe the case, that the rock marl can insensibly be traced into the state of mountain lime or schist, or gritstone;" and that these latter can also insensibly be traced into granite, and syenite, and the various forms of hornblende rock; and, lastly, if all these rocks are found occasionally to alternate with each other, (and, if I am not misinformed, coal has been found under mountain lime, and mountain lime under even granite,) from all these facts I think it necessarily follows, that there is a connection between these rocks, which, if it does not justify us in classing them under one series, effectually prevents us from finding any fixed law of their suc. cession.

“I am happy in being able to add the following powerful authorities in support of the opinion above expressed. Dr. Mac CulIoch, in speaking of the usual division of rocks into primary, tran. sition, and fætz, is inclined to think that these are distinctions which are more easily made in the closet than in the field ; and argues, that different strata which alternate must be collectively considered as of cotemporaneous formation * Brogniart, in his account of the Cotentin, to which I have already referred, after having observed that granite and gneiss occur in a syenitic forma tion to the east of the Erzegebürge, and that this syenite overlies argillaceous schist, and even grauwacķe; that Haussman and Von Buch found in Norway zoophytic limestone under a formation con şisting of syenite, granite, porphyry, gritstone, and argillaceous schist; and lastly, that there seem to be very few granitic districts which can be referred to a primitive formation of granite, con cludes by saying, that at present there is a great difficulty in establishing a good division of the strata t.

“ Saussure again observes, that the mountains of St. Bernard are a mixture of various strata, which have hitherto been ranged in different orders; but that the complete intermixture of these different orders, particularly of slates with quartz rocks, appears to perfect the proof of what he has often suggested, that philoso. phers have been too hasty in classing different orders of mountains, and of establishing precise limits between primitive and se. condary strata. It appears evident, he adds, thať nature has not assumed those divisions for the rule of her operations; and that, if she has not made mountains of granite, strictly so called, incumbent on calcareous foạndations, she has at least frequently mixed calcareous rocks and argillaceous schists with quartzose and mica ceous schists $; and in closing his account of the rocks of Mont Blanc, he says, it cannot be too often repeated, that we may exé pect to find, and do actually find in the mineral kingdom, all kinds

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"* Geological Transactions, vol. ii. p. 410."
6 + Cotentin, p, 25." "Şaussure, tom. iv, p. 264, 265."

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of mixtures in all kinds of proportions: whence arises an infinity of mixed and indeterminate species *.P. 130.

It will be readily acknowledged by every candid Wernerian, that there are exceptions to the regularity of succession in the strata of all the formations; that some members of the series are occasionally absent ; that the component parts are combined in different proportions; and, above all, that there exist a thousand proofs of violence and convulsion. Before the waters had finally retired, they appear to have made considerable impression even upon some portions of the first formation; and it would seem that the precipitations also of the primitive substances themselves, were occasionally disturbed by the agitated state of the great solvent. The principal point however, which every geognost should labour to ascertaiu is, whether there are not formations of such distinct characters, and of such universal distribution, as prove that they must have proceeded from a general cause. Now, it cannot be denied that the primitive mountain-rocks of Werner are seen in every quarter of the globe, in Europe, in China, in Van Diemen's land, in Brazil, Mexico, and Canada, at the Cape of Good Hope, and in Bengal, occupying the same relative position, and composing the most elevated parts of the earth's surface. Granite, indeed, is not in every instance followed by gneiss, mica-slate, and clay-slate: there may be a gap in the succession occasioned by accidental causes, but the order is never reversed, and their geological relations are every where the same. Be it observed, however, that we speak of primitive granite, highly crystallized and des titute of all organic remains; for there is a granite of a newer formation, which is found connected with transitive rocks, and which perhaps may occasionally contain both shells and vegetables. It must not be concealed, notwithstanding all this, that it is, in many cases, extremely difficult, and in some cases totally impossible, to nark where the primitive rocks terminate, and the secondary commence; and this is a circumstance which the very conditions of the Wernerian theory would lead us to exo pect. The precipitations which formed the primitive rucks, be it remembered, are not represented as having been entirely stopped when the transition class was begun; 'it is merely said that the quantity of the particular matter of which the former is composed, felspar, quartz, and mica, had considerably dimi. nished, and that the inechanical depositions were beginning to take place. The gray

wacke of the transition firmation is ree garded by the Wernerians as the product of deposition, but

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" Saussure, tom. iv. p. 469.'!

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