V.] THE ORIGIN OF MOUNTAINS. 57 



Jour. Geol. Society, Nov., 1859 ; Canadian Naturalist, Dec., 

 1859 ; Amer. Jour. Sci. (2), XXX. 136 ; and ante, page 9.) 

 , This hypothesis, as we have endeavored to show, is not only 

 completely conformable with what we know of the behavior 

 of aqueous sediments impregnated with water and exposed to 

 a high temperature, but offers a ready explanation of all the 

 phenomena of volcanoes and igneous rocks, while avoiding 

 the many difficulties which beset the hypothesis of a nucleus 

 in a state of igneous fluidity. At the same time any changes 

 in volume resulting from the contraction of the nucleus would 

 affect the outer crust through the medium of the more or less 

 plastic zone of sediments, precisely as if the whole interior 

 of the globe were in a liquid state. 



The accumulation of a great thickness of sediment along a 

 given line would, by destroying the equilibrium of pressure, 

 cause the somewhat flexible crust to subside ; the lower strata 

 becoming altered by the ascending heat of the nucleus would 

 crystallize and contract, and plications would thus be deter- 

 mined parallel to the line of deposition. These foldings, not 

 less than the softening of the bottom strata, establish lines of 

 weakness or of least resistance in the earth's crust, and thus 

 determine the contraction which results from the cooling of 

 the globe to exhibit itself in those regions and along those 

 lines where the ocean's bed is subsiding beneath the accumu- 

 lating sediments. Hence we conceive that the subsidence 

 invoked by Mr. Hall (and by Lyell), although not the sole 

 nor even the principal cause of the corrugations of the strata, 

 is the one which determines their position and direction, by 

 making the effects produced by the contraction not only of 

 sediments, but of the earth's nucleus itself, to be exerted along 

 the lines of greatest accumulation 



On the subject of igneous rocks and volcanic phenomena, 

 Mr. Hall insists upon the principles which we were, so far as 

 we know, the first to point out, namely, their connection with 

 great accumulations of sediment, and that of active volcanoes 

 with the newer deposits. We have elsewhere said : " The 

 volcanic phenomena of the day appear, so far as we are aware, 

 3* 



