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CONCEPCION. [chap. xiv. 



necessarily consequent on the tension of the land when upraised, 

 and their injection by fluidified rock. This rending and injec- 

 tion would, if repeated often enough (and we know that earth- 

 quakes 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 undero-oing 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, 1 believe that it 

 is impossible to explain the structure of great mountain-chains, 

 such as that of the Cordillera, where the strata, capping the in- 

 jected 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 in- 

 jected, 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 in- 

 verted 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.* 



* For a full account of the volcanic phenomena which accompanied the 

 earthquake of the 20th, and for the conclusions deducible from them, I must 

 refer to Volume V. of the Geological Transactions. 



i 



