XIV • AREA OF VOLCANIC ERUPTION 333 



The space, from under which v^olcanic matter on the 20th 

 was actually erupted, is 720 miles in one line, and 400 miles 

 in another line at right angles to the first ; hence, in all proba- 

 bility, a subterranean lake of lava is here stretched out, of 

 nearly double the area of the Black Sea. From the intimate 

 and complicated manner in which the elevatory and eruptive 

 forces were shown to be connected during this train of phe- 

 nomena, we may confidently come to the conclusion that the 

 forces which slowly and by little starts uplift continents, and 

 those which at successive periods pour forth volcanic matter 

 from open orifices, are identical. From many reasons, I believe 

 that the frequent quakings of the earth on this line of coast 

 are caused by the rending of the strata, necessarily consequent 

 on the tension of the land when upraised, and their injection 

 by fluidified rock. This rending and injection would, if repeated 

 often enough (and we know that earthquakes repeatedly affect 

 the same areas in the same manner), form a chain of hills ; — 

 and the linear island of St. Mary, which was upraised thrice 

 the height of the neighbouring country, seems to be undergoing 

 this process, I believe that the solid axis of a mountain differs 

 in its manner of formation from a volcanic hill, only in the 

 molten stone having been repeatedly injected, instead of 

 having been repeatedly ejected. Moreover, I believe that it 

 is impossible to explain the structure of great mountain- 

 chains, such as that of the Cordillera, where the strata, 

 capping the injected axis of plutonic rock, have been thrown 

 on their edges along several parallel and neighbouring lines 

 of elevation, except on this view of the rock of the axis having 

 been repeatedly injected, after intervals sufficiently long to 

 allow the upper parts or wedges to cool and become solid ; 

 — for if the strata had been thrown into their present highly- 

 inclined, vertical, and even inverted positions, by a single blow, 

 the very bowels of the earth would have gushed out ; and 

 instead of beholding abrupt mountain-axes of rock solidified 

 under great pressure, deluges of lava would have flowed out at 

 innumerable points on every line of elevation.^ 



1 For a full account of the volcanic phenomena which accompanied the earth- 

 quake of the 20th, and for the conclusions deducible from them, I must refer to 

 Volume V. of the Geological Ti-ansaclions. 



