1856.1 SCROPE — CRATERS AND LAVAS. 349 



me sufficient to account for most of the phsenomena of the kind ob- 

 servable in mountain-chains. 



These were the ideas on this subject which I endeavoured to de- 

 velope, though very imperfectly I am aware, in the more theoretic 

 portion of my work on volcanos, so often referred to, and they were 

 illustrated by a rude ideal section of an elevated 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 paroxys- 

 mal and simultaneous, or gradual, taking place by minor and success- 

 ive expansive throes or shocks, or even still more slowly in the man- 

 ner of a creep, as Sir Charles Lyell would probably conceive it to 

 have operated, and to be still continuing. On these last assumptions, 

 the earthquake-shocks which certainly accompany at present every 

 eifort of elevation, and appear to be propagated in waves through the 

 substance of the earth's crust, in directions usually at right angles to 

 the principal axes of elevation, or fissures of crystalline protrusion, 

 may indicate the force by which the extreme replications and slaty 

 cleavage of the laminated beds are occasioned. 



I would ask of geologists to consider whether such a mode of pro- 

 trusion of the laminated crystalline rocks and of the lateral replica- 

 tion of the more earthy schists and marine strata, as is here suggested, 

 does not accord with the general facts known respecting their posi- 

 tion ? Let me take two descriptions of the general position of the 

 crystalline rocks from two writers of experience, judgement, and 

 wholly impartial character, as respects the theory here indicated. 

 Mr. Evan Hopkins* gives as the results of his extensive mining ex- 

 perience in the Andes and elsewhere, "that 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 gra- 

 dations 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 forming, 

 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 cry- 

 stalline mass. 



Mr. E/Uskin, in his recently published volume, having closely ex- 

 amined the structure of the Alps with the eye of a geologist no less 

 than of a painter, but certainly without any theory to support, de- 

 clares 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 ultimately mica- and 

 chlorite -schists. 



One point observed in the structure of the Alps and many other 



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



2 B 2 



