Penny Blood: Serial Sensation and Working-Class Entertainment — page 302: what you’re looking at

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

CH, XXII. ] SUMMARY. 285 _ In order to arrive at some conclusion regarding the amount of force, with which the lava would be elevated in an open chasm, we have made a supposition respecting the constitution of the magma from which it is derived. Some late experiments by Mr Hannay, since published’, appear to warrant our as- sumptions. We suppose the state of igneo-aqueous solution to be such as has been already described in VIII., and that dimi- nition of pressure allows the water-substance to separate from the lava. This will rise through the column of lava and pro- duce ebullition. But in our calculations we have omitted the consideration of this ebullition, and supposed the water-sub- stance to remain in the identical mass of lava, simply expand- ing when separated from it by diminution of pressure. If the magma contains one-tenth of water in a given volume, it would be capable of thus rising to the summit of a lofty cone. And if a fissure was to be opened to the surface, the mean pressure of the lava upon the sides of it would be that of the weight of a column of rock about twelve miles high. This however would not be sufficient to produce compression, for which we must look to the pressure of the gas or vapour, confined in closed fissures, which at its maximum would be twice as great. The work of compression would be chiefly expended in de- forming the materials of the crust, producing cleavage and so forth, the work of raising the mountains, and depressing their roots into the fluid substratum, being comparatively small. The ease with which masses of rock would move over surfaces of dislocation, once established and lined with slickenside, wou'd appear to render regions, once disturbed, more liable than others to further disturbance. The quantity of igneous rock subsequently injected into the fissures would go to in- crease the solid crust in the disturbed regions, and, with the estimate we have already made, that the compression amounts to about two per cent., one-fiftieth of a vertical section through ‘the crust ought to be occupied by dykes, But it must be remembered that these would be most numerous and widest in the lower side, so that much of them would never come under observation. 1 See p. 276, and p. 277, note. COLA @ NOO (CO)