G. P, Scrope on Craters, and the Liquidity of Lavas. 229 



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mountain chain in the frontispiece to the volume. I still think 

 they will be found a not improbable solution of this the greatest 

 problem in the dynamics of geology. It appears to me, that 

 the results would be much the same, whether we suppose this 

 elevatory action to have been jMroxysmal and simultaneous, or 

 gradual, taking place by minor and successive expansive throes 

 or shocks, or even still more slowly in the manner of a creep, as 

 Sir Charles Lj^ell would probably conceive it to have operated^ 

 and to be still continuing. On these last assumptions, the earth- 

 quake-shocks which certainly accompany at present every effort 

 of elevation^ and appear to be propagated in waves through the 

 substance of the earth's crust, in directions usually at right an- 

 gles to the principal axes of elevation, or fissures of crystalline 

 protrusion, may indicate the force by which the extreme replica- 

 tions and slaty cleavage of the laminated beds are occasioned. 



I would ask of geologists to consider wdiether such a mode of 

 protrusion of the Liminated crystalline rocks and of the lateral 

 replication of the more earthy schists and marine strata, as is 

 here suggested, does not accord with the general facts known re- 

 specting their position? Let me take two descriptions of the 

 general position of the crystalline rocks from two writers of ex- 

 perience, judgment, and wholly impartial character, as respects 

 the theory here indicated. Mr, Evan Hopkins* gives as the re- 

 sults of his extensive mining experiences in the Andes and else- 

 where, 'Hhat the great base [of all mountain chains] is below 

 more or less granitic, strongly saturated with mineral waters, 

 and that this passes upwards" by insensible gradations from a 

 crystalline homogeneous compound into a laminated rock, such 

 as gneiss, and still higher up into schists in vertical planes ; the 

 peculiar varieties of the higher rocks depending on the mineral 

 character of the 'parent rock' below; the schistose rocks form- 

 ing, in short, the external terminations of the great universal 

 crystalline base,"— that is to say (as I would phrase it,) the 

 squeezed out, and therefore laminated, upper and lateral portions 

 of the inferior crystalline mass. 



Mr. Ruskin, in his recently published volume, having closely 

 examined the structure of the Alps with the eye of a geologist 

 ^o less than of a painter, bat certainly without any theory to 

 support, declares that the central axes of 'irregular crystallines" 

 (as he calls the granitic rocks) uniformly graduate on either side 

 into the foliated or ''slaty crystallines," i e., into gneiss and ulti- 

 mately mica and chlorite-schists. 



One point observed in the structure of the Alps and many 

 other mountain chains I may notice before ^ conclude, namely, 

 the occasional dip of the elevated strata towards the central axis 

 of extruded crystalline rock, producing a synclinal, instead of 



Quart. Journ. Geol Soc, vol. xi, p. 144. 



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