Rev. Mr Whewell^s Address to the Geological Society. 161 



supposition that there are, beneath the crust of the terrestrial 

 globe, liquid or semiliquid masses which exert a pressure up- 

 wards, leads to the inquiry what phenomena of fissure, disrup- 

 tion, and dislocation, this subterraneous strain would produce- 

 The answer to this inquiry must be given by mathematical 

 reasoning from mechanical principles ; and Mr Hopkins, who 

 proposed, and to a considerable extent solved this problem, has 

 put forth a set of results, with which, so far as they are defi- 

 nite and decisive, it will be highly important to compare the 

 existing phenomena of disturbed geological districts. The 

 same assumption, of an incandescent mass existing deep below 

 the earth'*s surface, has led two other distinguished members of 

 our body to another train of speculations ; which, however, 

 though highly interesting, I should be disposed to consider as 

 only the enunciation of a problem, requiring no small amount 

 of mathematical skill for its solution. I speak of the specula- 

 tions of Professor Babbage and Sir John Herschel, concerning 

 the subterraneous oscillations of the isothermal surfaces of 

 great temperature. They remark that such oscillations will 

 arise, when thick and extensive deposits take place on any 

 parts of the surface of the earth (as for instance at the bottoms 

 of seas), because such deposits increase the thickness of the 

 coating over a given subterraneous point ; and thus removing 

 the cooling effect of the surface, bring a high temperature to a 

 place where it did not exist before. The deposited strata 

 might thus be invaded by violent heat advancing from below ; 

 and there might result both changes of position arising from 

 extension and contraction, and a metamorphic structure in the 

 rocks themselves. It is highly instructing to have this chain 

 of conceivable effects pointed out to us ; but we may venture to 

 observe that, in order to render the suggestion of permanent use, 

 it will be necessary to express, in some probable numbers, the 

 laws of the result as affected by the conductivity of the earth's 

 mass, the rate and thickness of the deposit, and other circum- 

 stances. For instance, we know that a deposit of one thousand 

 feet thick would be quite insufficient to occasion a metamor- 

 phic operation in its lower strata. Would, then, a deposit of 

 ten thousand or of twenty thousand feet call into play such a 

 process .? To answer questions like these, of which a vast num- 



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