Penny Blood: Serial Sensation and Working-Class Entertainment — page 272: 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. 255 activity ascended gradually to regions at less distance from the surface. There is within the limits of conjecture based on physical laws, no lack of processes which could co-operate to that effect. The consolidation of the ejected masses within the fissures would probably proceed simultaneously, by loss of heat, from the surface downwards and, by pressure, from below upwards, The opening of new branches from the main fractures, the remelting (by the aid of the heat of the molten mass within the latter, and of water finding access to it) of solidified matter adjoining the fracture, the emission of that remelted matter through those branches: all these are secondary processes depending on the first almost necessarily. The sup- position that to those 1s due the order of time in which trachyte and rhyolite have been ejected to the surface, is corroborated by the fact that these rocks occupy generally a subordinate position in regard to quantity and have had to a great extent their origin in volcanic action ”—that 1s, as distinguished from massive or fissure eruption. It is clear that, in order to obtain the acid magma required for the production of the eruptions of trachytic rocks subsequently to the andesitic, some method must be devised to explain the refusion of the granitic crust, lying, already consolidated, above the andesitic magma. Richt- hofen proposes to do this by “the aid of the heat of the molten mass” within the main fracture, “and of water gaining access to it.” This appeals to the very doubtful hypothesis already referred to, which supposes “ glowing lava,” not already liquid, to absorb water admitted to it from without, and thereby to become liquid and light. Moreover it requires the “molten mass within” the fissure to contain an excess of heat sufficient to melt an additional mass of a more refractory rock than itself. But it is evident that 1t could not transfer more than so much of its own heat to another mass, as would raise the two to a common temperature, less than its former temperature. Captain Dutton’s discussion of the same sequence is interest- ing and instructive, and well worthy of study, but still not satis- factory. The general principles employed by him are indicated in the following sentence: “In order that any eruption of lava may take place two preliminary conditions are requisite. First, GONG oOo SS (CO)