

ACTION OF VOLCANOES. 381 



volcanoes have been in constant action since the dawn 

 of history, and long before it, yet the elevation of hills 

 by their agency has always been a very slow and 

 partial process. The history of the best known volcanoes 

 is decisive as to this. Therefore as a factor in the 

 creation of mountain ranges, their action may be regarded 

 almost as infinitesimal. Moreover so far as is known, 

 except in the case of a certain number of peaks in the 

 Andes and some few others, very few of the highest moun- 

 tains have ever been volcanoes, also the high ridges 

 and peaks of the majority of mountain ranges are very 

 generally known to consist of the plutonic, and not of 

 volcanic rocks. 



Now at the time when these rocks burst through 

 the overlying sedimentary strata, in the way described, 

 the edges of the latter were forcibly bent up on 

 each side of the gap, so as to form, as they do 

 now, the exterior and lower slopes of the mountains, 

 which rest upon the core of older crystalline rocks, 

 thus forced up through them ; and so, as we humbly 

 venture to suggest, the great systems of mountain 

 ranges upon our earth were originally built up. 



It is however true that instances may be cited where 

 the older sedimentary rocks are found occasionally 

 occupying positions on the tops of mountains, and the 

 interpretation we should be inclined to put upon that 

 fact is, that these rocks were in such cases simply 

 bulged up by the force from below, which would seem 

 at that point to have lacked sufficient power to burst 

 through, and so therefore did not pierce the superin- 

 cumbent mass. In other cases where an enormous 

 display of force seems to have manifested itself, and 

 where in consequence the upheaval of two or more 





