68 



ON GEOLOGl. 



must be so enormously compressed, as not only to render them easili 

 fused, but in many instances to prevent their volatilization after the fusion 

 has taken place ; and from this circumstance it is possible, we are told, to 

 explain a variety of appearances and qualities in minerals, and to answer 

 a variety of objections which would otherwise weigh heavy against the 

 general theory. 



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

 the means by which they are supposed, upon this theory, to be accom- 

 plished, there seems to be no very serious objection. It is as readily 

 allowed by the Neptunian as by the Plutonic geologist, 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 limestone, and through which are distributed veins of crys- 

 tallized carbonate of hme, together with a variety of similar facts, fatally 

 mihtate against the agency of heat as an universal cause ; since, in such 

 case, allowing it to have iDeen sufficient to produce the general effect of 

 crystaUization, 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. Play- 

 fair'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 ex- 

 tent supposed in the theory before us, as combustion itself, which is relin- 

 quished 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 struc- 

 ture, the universality of its application, the plausibility of its appearance, 

 and the talents with which it has been supported, it is built upon assump- 

 tion alone ; it lays down principles 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 

 opposed, and which, as 1 have already observed, is denominated the Nep- 

 tunian. 



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 hydrogene and oxygene, 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 materials thus held in solution granite is supposed to have been 

 produced first, and in by far the greatest abundance. It hence, consoli- 

 dated 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 consists, as we have already observed, of felspar, 

 quartz, and mica, all which must therefore have concreted by a crystalhza- 

 tion 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 

 arid vegetable kingdoms. All the other rocks, upon this hypothesis, began 



