ON GEOLOGY. 



75 



To the principle of an alternate decay and renovation, separated from the 

 means by which they are supposed, upon this theory, to be accomplished, 

 there seems to be no very serious objection. It is as readily allowed by the 

 Neptunian as by the Plutonic geolog-ist, that the strata of the earth are liable 

 to waste, and are, indeed, perpetually wasting ; and that the waste materials 

 are carried forward to the sea. But the appearance of shells in limestone 

 and marbles, in which the sparry structure is as perfect as in primary lime- 

 stone, and through which are distributed veins of crystallized carbonate of 

 lime, together with a variety of similar facts, fatally militate against the 

 agency of heat as a universal cause ; since, in such case, allowing it to have 

 been sufficient to produce the general effect of crystallization, every vestige 

 of the structure of the shells must have been destroyed, and every atom of 

 the carbonic acid totally evaporated. 



It is, secondly, useless to argue, that there are other sources of heat than 

 combustion or deflagration; because, admitting the fact to Mr. Playfair's 

 utmost desire, it can be satisfactorily proved that all these sources are as 

 little capable of acting in the interior parts of the globe, to the extent sup- 

 posed in the theory before us, as combustion itself, which is relinquished by 

 its defenders as incompetent to their purpose. But even allowing the full 

 operation of all, or of any one of these causes, we have no method pointed 

 out to us by which this subterranean heat is duly preserved and regulated — 

 no controlling power that directs it to the proper place at the proper season, 

 without which it must be as likely to prove a cause of havoc and disorder as 

 of renovation and harmony. It is useless, therefore, to pursue this theory 

 any farther. In spite of the magnificence of its structure, the universality 

 of its application, the plausibility of its appearance, and the talents with which 

 it has been supported, it is built upon assumption alone ; it lays down prin- 

 ciples which it cannot support, and deals in fancy and conjecture rather than 

 in solid facts and firm evidence. 



Let us next, then, take a glance at the theory by which this is chiefly op- 

 posed, and which, as I have already observed, is denominated the Neptunian. 



Under this hypothesis, the two substances that were first evolved out of the 

 general chaos on the formation of the earth, and chemically united to each 

 other, were hydrogen and oxygen, in such proportion as to produce water, 

 which is a compound of these substances, and in such quantity as to be able 

 to hold every other material in a state of thin paste or solution. Of the ma- 

 terials thus held in solution granite is supposed to have been produced first, 

 and in by far the greatest abundance. It hence, consolidated first, probably 

 forms the foundation of the superficies of the globe, and perhaps the entire 

 nucleus of the globe itself; and, as has been already seen, while it constitutes 

 the basis of every other kind of rock, rises higher than any of them. It con- 

 sists, as we have already observed, of felspar, quartz, and mica, all which 

 must therefore have concreted by a crystallization nearly simultaneous ; and 

 from its containing no organic remains, it is obvious that it must have been 

 formed prior to the existence of the animal and vegetable kingdoms. All the 

 other rocks, upon this hypothesis, began to crystallize and consolidate after 

 the formation of granite, in the order in which we have already traced them ; 

 and some of these before the whole of the granite was rendered perfectly 

 firm, whence we trace beds of several of them in the granite formation itself ; 

 and as the same kind of action appears to apply to the whole, we, in 

 like manner, trace beds of the newer rocks successively in formations of those 

 that are older; and, at last, remains of animal and vegetable materials, which 

 are hence proved to have had an existence coetaneous with the newer classes. 



The law of gravity appears to have operated through the whole of this pro- 

 cess ; and hence water, as the least heavy material, must have risen to the 

 surface, and purified itself by a filtration through the other materials, and at 

 kngth collected in such hollows as were most convenient for its reception: 

 these hollows constitute the bed of the ocean. 



Water, thus collected in the cavity of the ocean, is carried by the atmos- 

 phere over the tops of the most elevated mountains, on which it is precipi. 



