Penny Blood: Serial Sensation and Working-Class Entertainment — page 206: what you’re looking at

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

cH. xv.] COMPRESSION AND VOLCANIC ACTION. 189 It is probably to this kind of action that we may attribute the opening of fissures radiating from volcanic vents, along which subsidiary craters are established. Thus for instance an earthquake, caused by a volcanic explosion in Iceland on the 4th January, 1875, “opened rifts forty miles in length in the plains north of Dy¥ngjufjoll, and it was from fissures in a tract twenty miles in length and about three in breadth, which sank to some depth between two of these rifts, that the lava welled forth’.” If however the water-substance should not be able to escape from the magma sufficiently rapidly for the vapour pressure to accumulate so as to prevent the magma from almost entirely occupying the fissure, or if the fissure should open to the surface so that the vapour above the fluid should escape, then the magma would rise into the fissure pressed upwards by the weight of the crust around the base of the ascending column. In this case it would not behave within the fissure like an inert liquid, for it would carry with it the water-substance which is one of its con- stituents, and that, when raised within the fissure, would have? an expansive force of its own, For this expansive force, although equalised at the bottom of the crust to the pressure of the crust, arises from the store of energy due to the temperature of the water-substance, and to whatever place it may be transferred it will carry that energy with it. In order to come to any conclusion about the amount of this force we must make some supposition concerning the constitu- tion of the magma, which for convenience we will call “lava” after it has risen into the fissure, retaining the name of magma for the fluid substratum. The supposition which we will make shall be that the magma consists of hot rocky matter in combination with super- heated water. In a given mass of the magma there isa certain proportion of rocky matter which is inelastic, and the remainder consists of water-substance at the same exalted temperature, the presence of which renders the magma elastic, and if the pressure were infinitely increased the whole would be reduced 1 “Volcanic History of Iceland,’’ by Mr W. G. Lock, sale Mag. Dec, 11., Vol. viz. p. 214. : ‘ COLA @ NOO (CO)