Penny Blood: Serial Sensation and Working-Class Entertainment — page 295: what you’re looking at

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

278 SUMMARY. (cH. xxII. X. We next attempt to deal with the condition of the earth’s crust just described. It will be observed that it is analogous to the case of a broken-up area of ice, refrozen and. floating upon water. The thickened parts which stand higher above the general surface also project deeper into the liquid below. We have supposed the crust to have the specific gravity of granite, and the fluid substratum to have that of basalt. Hence their ratio 1s about 0°905, whilst the specific gravity of ice is 09176. These numbers are so nearly the same that the cases are exceedingly analogous, and the down- ward protuberance of the crust, as compared with the elevations above the surface, will agree closely with the immersed part of an iceberg as compared with the part exposed. When the crust is crushed together along a mountain-range, part of the mass will be sheared upwards and part downwards. If it be equally rigid from top to bottom, half of it will go up and half of it down, and the neutral zone, as we have termed it, will be at half the depth. But, if the lower parts be softened by heat, a greater thickness will be sheared downwards than up- wards, If the softening were to follow a certain assumed law, which would make it increase slowly at first but more rapidly at last, until it mingled with the fluid substratum, the neutral zone would be at the depth of one-third of the crust. This would be probably an excessive estimate. We accordingly have assumed a value between the two and place the neutral zone at the depth of two-fifths of the whole thickness, And here we arrive at a stage at which we make our first attempt at estimating the actual thickness of the crust. Granite has been formed in the presence of liquid water. Water cannot remain a liquid at a higher temperature than 773° F., what- ever pressure may be placed upon it. This temperature, at the rate of increase of 1° F. for from 51 to 60 feet, would be found at the depth of from 7 to 84 miles. Hence rock, which was once at the depth of from 7 to 84 miles, has been forced up- wards; and therefore the neutral zone is not so deep as that. But if 2 of the thickness were 7 to 84 miles, the whole thickness would be from 17 to 21 miles. Hence we conclude the whole COMIC OOOKS.EO