Penny Blood: Serial Sensation and Working-Class Entertainment — page 219: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

202 COMPRESSION AND VOLCANIC ACTION. [cu. xv. water upon the buried sediments would be condensation, from the diminution of porosity and still more from the conversion of the earthy materials into crystalline species of higher specific gravity, thus causing contraction of the mass. <A further and very important result of this accumulation there pointed out was by the softening of the underlying floor, or the ‘buttom strata to establish lines of weakness or of least resistance tn the earth's crust, and thus determine the contraction which results from the cooling of the globe to exhibit rtself in those regions, and along those lines where the ocean's bed 1s subsiding beneath the accumulated sediments. Hence, I added, ‘we con- ceive the subsidence invoked by Mr Hall, though not the sole nor even the principal cause of the corrugations of the earth’s strata, 1s the one which determines their position and direction by making tbe 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’’’’. The theory so epitomised appears to have gained very general acceptance among physical geologists. But if the reason- ing of the earlier chapters of the present volume is correct, the cooling of the globe cannot be appealed to to furnish the requisite compression (in the above extract called “contraction”), much less would 1t furnish a sufficient balance of compression along a belt of crust, itself contracting through metamorphic action. But upon the view now suggested, the circumstances fit in very well. The thick deposit depressing the crust, in- duces metamorphism in its lower portion. This cracks in con- sequence. The magma fills those cracks with highly expansive vapour, and compression 1s the result. It is also important to remark, that the vapour pressure in a chasm would be increased when the crust was thickened, because the tension at the bottom of the crust is proportional to its thickness. On this account, although it would require a greater horizontal force to compress the crust where it 1s thicker, yet the requisite increase would be furnished to the force by the very fact of the increased thickness. If our theory of the 1 * American Journal of Science and Art,” 1873, Art. xxvit. p. 265. COMIC OOOKS.EO