Penny Blood: Serial Sensation and Working-Class Entertainment — page 288: what you’re looking at

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

CH. XXI1.] SUMMARY. 271 an unknown amount of the central parts being rendered solid by pressure. The downward increment of density is expressed by the chemical increment of the heavy bases: and the fluid region directly under the crust consists, first of a felspathic and acid magma, which passes downwards by successive replacement of bases into an augitic and finally, into a magnetitic magma. This theory appears to have a great deal to recommend it. _ Waltershausen has given the probable densities and pressures at different depths, but the formula by which he has calcu- lated them appears to be arbitrarily assumed. He makes the density at the centre of the earth 9°59, or about that of sil- ver, and the pressure there that of about 2,500,000 atmo- spheres. If, however, we use Laplace’s law of density, the pressure at the centre comes out considerably greater, reaching that of 3,000,000 atmospheres. There will be found given in the appendix a new theory of the constitution of the interior of the earth by M. Roche, which will satisfy the requirements of geology, provided the difficulty, connected with the change of rotational velocity, which we have suggested, can be satisfactorily met. IV. Having devoted the first three chapters to the con- sideration of the more general questions regarding the consti- tution of the earth as a whole, we now approach the geological aspect of the subject. The outer crust of the earth is the pecu- liar domain of geological enquiry. And enquiry leads to the conclusion that this crust has been subjected to great violence, being compressed, ruptured, raised, and depressed, and also subjected to heating. A special phenomenon of a most start-_ ling kind, did not frequency of description render us familiar with it, is that in certain districts, outbursts of fiery vapours and molten rock, accompanied by violent earthquakes, mark the volcanic regions of the surface. To account for both these classes of phenomena a source of energy is required, and to the earth’s interlor we must look to supply it. Here we find gravitation, and heat stored up ready for our purpose. How have these agents produced the results we witness? This is our problem. GONG oOo SS corm