Penny Blood: Serial Sensation and Working-Class Entertainment — page 215: what you’re looking at

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

198 COMPRESSION AND VOLCANIC ACTION. {[cu. xv. compact the rock, and render it more dense. But if the hori- ‘zontal were considerably to exceed the vertical, the rock would be sheared upwards and downwards. Whether the force at our disposal under the hypothesis now offered would be sufficient for this purpose is of course open to argument, but considering that, with time given, all known substances yield more or less to deforming forces, it seems quite possible that it may be so. And the facts which we shall bring forward presently make it almost certain that the work has been effected in this manner’. Moreover the rocks fissuring from contraction, will detract from their rigidity, and render shearing more easy, when large. volumes of them are under consideration. If our chasm did not extend upwards to the surface, when the tension of the vapour in it diminished through cooling the lava would ascend further, until it became too viscous to rise’ higher. At such a juncture we might have vapours still at a very considerable pressure occupying the upper portion of the fissure, while the lower part would be filled with the magma, solidified at its upper surface and more and more fluid below. In this manner we may conceive gaping chasms to have been . formed, which might be for a long time occupied by heated > { vapours, and gradually converted into mineral veins. When the molten rock injected by hydrostatic pressure into the fissures came to solidify into the dykes which so abundantly intersect metamorphic strata, it 1s probable that another efficient ' cause of compression would come into play, for, as already mentioned, the result of recent experiments appears to show that such substances as whinstone and granite are less dense in the solid than in the liquid state at the melting temperature’. In this respect then they behave like water. 1 pp. 203, 204. 2 p. 23. If this fact be established, then it appears that pressure lowers the melting temperature of such rock masses. But it has been considered proved that the greater portion of the globe is extremely rigid, and it has been considered to owe its rigidity to pressure, We must conclude then, either that the central part consists of materials of a different kind from those which have yielded these experimental results, or else that it is cool. The former sup- position is the more likely to be true. NOOKS COLA @ (CO)