412 Review of the Progress of 
the gradual contraction of the interior. An able discussion of 
this view will be found in the American Journal of Science [2] 
iii, 176, from the pen of Mr. J. D. Dana, who, in common with 
all others who have hitherto written on the subject, adopts the 
- notion of the igneous fluidity of the earth’s interior. — 
We have however elsewhere given our reasons for accepting 
the conclusion of Hopkins and Hennessy that the earth, instead 
of being a liquid mass covered with a thin crust, is essentially 
solid to a great depth, if not indeed to the centre, so that the 
voleanic and igneous phenomena generally ascribed to a fluid 
nucleus have their seat as Keferstein and after him Sir John 
Herschel long since suggested, not in the anhydrous solid un- 
stratified nucleus, but in the deeply buried layers of aqueous 
sediments which, permeated with water, and raised to a high 
temperature, become reduced to a state of more onless complete 
igneo-aqueous fusion. So that beneath the outer crust of sedi- 
ments, and surrounding the solid nucleus we may suppose a zone 
of plastic sedimentary material, adequate to explain all the phe- 
nomena hitherto ascribed to a fluid nucleus. (Quar. Jour. Geol. 
Society, Nov. 1859. Canadian Naturalist, Dec. 1859, and Amer. 
Jour. Sci. [2,] xxx, 136). 
i othesis, 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 of the phe- 
nomena of volcanos and igneous rocks, while avoiding the many 
difficulties which beset the hypothesis of a nuclens in a state of 
igneous fluidity. At the same time any changes in volume 
resulting from the contraction of the nucleus would affect the 
ing altered by the ascending heat of the nucleus would erystal- 
lize and contract, and plications would thus be determined paral- 
lel 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 con- 
traction 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 accumulating sediments. Hence 
we conceive that the subsidence invoked by Mr. Hall, although 
not the sole nor even the principle cause of the corrugations of 5 
the strata, is the one which determines their position and direc 
tion, by making the effects produced by the contraction, notonly = 
a a ae © 
