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years an opinion has taken root among us, that the dynamics of 

 geology must invoke the aid of mathematical reasoning and calcu- 

 lation, as the dynamics of astronomy did, at the turning point of its 

 splendid career. Nor can we hesitate to accept this opinion, and to 

 look forwards to the mathematical cultivation of physical geology, as 

 one of the destined stages of our progress towards truth. But we 

 must remember, that in order to pursue this path with advantage, 

 we have, in every instance, two steps to make, each of which 

 demands great sagacity, and may. require much time and labour. 

 These two steps are, to propose the proper problem, and to solve it. 

 Last year an important example of this kind was brought under your 

 notice by my predecessor. The supposition that there are, beneath 

 the crust of the -terrestrial globe, liquid or semiliquid masses which 

 exert a pressure upwards, leads to the inquiry what phEenomena of 

 fissure, disruption, 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 pro- 

 posed, and to a considerable extent solved this problem, has put forth 

 a set of results, with which, so far as they are definite and decisive, 

 it will be highly important to compare the existing phsenomena of 

 disturbed geological districts. The same assumption, of an incandes- 

 cent 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 specu- 

 lations of Professor Babbage and Sir John Herschel, concerning the 

 subterraneous oscillations of the isothermal surfaces of great tem- 

 perature. 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 de- 

 posited 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 concei- 



