16 Essay introductory to Geology. 



THEORETICAL GEOLOGY. 



Thus far we have abstained from all theoretical inferences, which the 

 most sceptical could tax with any shadow of gratuitous assumption, and 

 dealt simply in pure description. The error, if error there has been, must 

 therefore, up to this point, have consisted in positive false statement : 

 there has been no possible opening for delusive reasoning. Yet whoever 

 has weio-hed this description, if he barely allows it to have been accurately 

 given, must surely be struck at the overwhelming mass of novel and 

 astonishing facts which this science, in its very elemental observations, 

 places before his view ; and he inust feel that many of these facts necessa- 

 rily carry with them the most direct evidence of those theoretical infer- 

 ences, which before perhaps he ignorantly considered as the arbitrary 

 fictions of visionary dreamers, scheming how they might construct after 

 their own imaginations. These inferences he must now perceive are, to 

 a very great degree, the necessary conclusions of the soberest interpreta- 

 tion of nature, — never assumed k priori, but carefully deduced a posteriori. 



In the first place, he will at once perceive that nine-tenths of the 

 existing continents have originally been buried many fathoms beneath the 

 bosom of the primreval ocean. He must therefore of necessity seek to 

 account in some manner for this great change of level between the land 

 and water. And here only two possible classes of hypotheses present 

 themselves, of which one or the other alternative must be true : — either 

 the water has in great measure disappeared, througii chemical decomposi- 

 tion, by becoming fixed in some of the deposited minerals, and the like ; 

 or else a relative change of level must have been mechanically effected, by 

 forces tending to elevate the masses of the continents, or depress the 

 receptacles of the oceans. Now of the chemical hypothesis he will find no 

 evidence, and it must rest entirely on gratuitous assumptions. With 

 regard to the mechanical hypothesis, he will argue, if this be true, the 

 strata must necessarily iiave undergone great disruptions and dislocations. 

 He will proceed to examine them with this view, and on his examination, 

 he will find that they do actually present the very phenomena he had 

 anticipated as necessary conditions of the mechanical hypothesis. — Vide 

 Supra III., Sec. 1 and 2. 



Allowing, then, the probable conclusion in favour of the mechanical 

 elevation of the continents, he may further desire to enquire whether this 

 operation has gone on uniformly, or been attended by oscillations. In 

 answer to this enquiry, he will again proceed, not by gratuitous assump- 

 tion, but by carefully interrogating facts, and examining the phenomena. 

 The present writer believes the answer he will obtain will be in favour of 

 considerable oscillation. His induction maybe imperfect; but assuredly 

 his conclusion is not gratuitous. Again, the enquirer may reasonably 

 demand what would be the probable effects of this process of elevating the 



