Penny Blood: Serial Sensation and Working-Class Entertainment — page 259: what you’re looking at

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

242 THE YOLCANO IN ERUPTION. (CH, XIX. to the volcanic foci have already been pointed out’, and it seems hard to believe that the mode of action here described can have a real existence. Moreover Richthofen appeals to the cooling of the globe as the ultimate cause, of which cause we claim to have proved the inadequacy. He says, “elevations and eruptive activity, even when locally not quite coincident, are co-ordinate effects of the cooling of the globe; but while the one is its immediate effect, the other results from it only by the concurrence of other agencies, which by themselves alone would have been incapable of producing results of such mag- nitude.” The memoir from which these passages are taken is of great interest, and contains many very suggestive obser- vations, and sage generalisations well worthy of study. On the whole his theory of volcanic action approaches more nearly than any other to that which we now advocate. We have already indicated in a general way the manner in which we would explain the phenomena with such a crust as we have supposed, subject to disturbances from transference of sediment, and consequent local depression. The contraction of the lower parts of the crust, where it becomes depressed into regions of higher temperature, will induce metamorphism, and shrinking, and shrinking will cause fissuring. Changes in the distribution of load by transference of sediment will also have a tendency to produce fissures, and it has been pointed out how these, commencing below, may be propagated until they reach the surface, and become filled with lava, in which the expansion of the water-substance, at a temperature far above the critical point, will render the column of molten rock on the whole specifically lighter than the mean crust, so that it will escape at the surface. In a general way this seems probable, but we have already shown that, under certain admissible suppositions, what we have just stated will necessarily occur. It is true that we have con- sidered the problem only as a statical one, for the ascent of vesicles of water through the lava, causing ebullition at the surface, has not been taken account of, but merely the decrease in density of the lava upwards, caused by the expansion of 1 p. 90 et seq. ° COMIC OOOKS.EO