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vable eiFects 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 de- 

 posit, and other circumstances. For instance, we know that a deposit 

 of one thousand feet thick would be quite insufficient to occasion a 

 metamorphic 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 number 

 must at once occur to our minds, we have many experimental data to 

 collect, many intricate calculations to follow out. And it would be 

 easy to point out problems of a still more abstruse kind, in which 

 we no less require aid from the mathematician, before we can proceed 

 in our generalizations. May we not hope to see some fortunate man 

 of genius unveil to us the mechanics of crystalline forces ? And 

 when that is done, can we doubt that we shall have a ray of new 

 light thrown upon those extraordinary phsenomena of slaty cleavage 

 in mountain masses which have lately been brought under our notice ? 

 Or, recollecting the experiments of Sir James Hall, (a striking step 

 in geological dynamics,) may we not hope then to learn how those 

 crystalline forces are stimulated by heat ; and thus follow the meta- 

 morphic process into its innermost recesses ? These and a thousand 

 such questions lie before us ; — tangled and arduous inquiries no doubt, 

 but connected by their common bearing upon one great subject ; — ' a 

 mighty maze, but not without a plan.' And through this maze we 

 must force our way in order to advance towards any sound geological 

 theory. The task is one of labour and difficulty ; but I well know, 

 gentlemen, that you wiU not shrink from it on that account. Those 

 who aspire to the felicity of knowing the causes of things, must not 

 only trample under foot the fears of a timid unphilosophical spirit, 

 which the poet deems so necessary a preparation, but they must look 

 with a steady eye upon difficulty as well as violence. They must 

 regard the terrors of the volcano and the earthquake, the secret 

 paths by which hot and cold and moist and dry ran into their places, 

 the wildest rush of the fluid mass, the latent powers which give so- 

 lidity to the rock, — as operations of which they have to trace the laws 

 and measure the quantities with mathematical exactness. And though 

 there can be no doubt that the greater part of us shall be more use-. 



