Penny Blood: Serial Sensation and Working-Class Entertainment — page 268: what you’re looking at

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

cH. xx.] SEQUENCE OF VOLCANIC ROCKS. 25! Consequently the force below > = < force above, d p*{l —(o— ale as—- >a {ft h e —1)(«—p)" or, with the usually assumed values of p and oa, as | : >=<37. But | f cot 6; ;, ; and 3°7 =cot 15° nearly; and cot 6 > cot 15° if 6 < 15° Hence, when the angle of inclination of the mountain is less than 15°, the force beneath, which urges the melted rocks along the surface of the root, will be greater than that which would urge a liquid along the surface of the mountain vertically above it. Hence, by comparing it with the behaviour of ,subaerial lava, we can see that the tendency for the rock fused off the root to spread itself beneath the crust will be considerable. We shall therefore have beneath the bottom of the crust areas where the matter fused off the roots of the mountains, and more or less mingled with the denser substratum, is spread out. It is probable that these areas will be local, and not extend beyond a certain distance from the roots of the ranges. They will be analogous to the alluvial deposits, which cover the plains of the upper world. When an eruption occurs above any of these areas, this fused matter will be the first to be ejected, mingled with water-subs.ance already imparted to it by diffusion from the magma beneath it; and, if this fused matter is supplied sufficiently rapidly, it will be the only kind of rock ejected, except such as may be derived from the sides of the funnel. Having been derived from the material of the roots, and in its flow mixed with the denser magma in various proportions, the resulting lava will conform to the law of Bun- sen, which asserts that all eruptive rocks are compounded of GONG oOo SS (CO)