Penny Blood: Serial Sensation and Working-Class Entertainment — page 231: what you’re looking at

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

214 ON FAULTING. [cH. XV bottom, on account of the direction of the hade, it seems that the fissure will be kept closed, and not admit the magma from below. If however the contraction were very nearly equal on both sides of the fissure, so that there was no greater settlement on one side than on the other, a fissure might be actually opened downwards through the whole thickness of the crust; and being open above so as not to form a chamber for the accumulation of ‘high-pressure vapour to prevent it, the magma would rise into it, and one of those great fissure eruptions would ensue, which have, at one or another geological epoch, covered large portions of the globe with beds of igneous rock. The notion of a vast crevasse extending downwards to the fluid magma may seem a wild dream, and certainly has no parallel in anything known to occur at the present day. But neither has any event of the nature of a fissure eruption come under the cognizance of man; and yet their former occurrence seems incontestible. And consequently the existence of such fissures becomes a necessity °. The datum-level equation, (1) p. 47, is at once made ap- plicable to the case of faulting, when that arises from con- traction of the rocks, by making e negative. But since the rocks are supposed to contract in the vertical as well as in the horizontal direction, e will represent the quadratic contraction of the vertical section; that is to say, upon the contraction taking place, the sectional area 41 will become the area kl(1—e). We shall then have, kle = (b) — & (a) + & (a) — 3 (8). It is easily seen that this is correct, because the area of vertical section, which was before contraction occupied by él, is after contraction occupied by kl (1—e) +3 (b)—% (a) +3 (a) -3(8); 1 «The Lava Fields of North Western Europe,” Prof. A. Geikie. Nature, Vol. xxix. p. 8. 1880. Also Richthofen’s ‘‘Natural System of Volcanic rocks,” p. 17. Mems. of California Academy of Sciences, Vol. 1. Pt. ii. San Francisco, 1868. COMICOOOLKS @ (CO) —_ — . yee SO