156 



ON THE ORIGIN OP MOUNTAIN RANGES. 



'■' It is evidoTit, on very littlo oorisidcration, iliafc ill is mass 

 of rock cannot expand laterally, for in that case it would 

 displace the crust of the earth surrounding the affected 

 area; nor downwards, for that would displace tlio solid 

 foundations of the earth itself. It is only free to expand 

 upwards. We may therefore take it that the lateral in- 

 crease of volume will be transformed into an upward one. 

 The lower strata would expand the most, the surface would 

 not expand at all. The behaviour of the crust under these 

 conditions would depend on the nature of the strata affected. 

 If the beds wore comparatively thin, they would become 

 folded and packed together in a more or less vertical posi- 

 tion. The internal strain would have most effect in the 

 region of least expansion, and the packing of tlio strata in 

 this locus would ridge up the surface and burst it along the 

 lines of greatest weakness, for the surface layers would be 

 unaffected by the subterranean heat." 



Mr. Reade contends that under the intense pressni'os tlius 

 generated, even the hardest rocks, such as consolidated 

 granites, whinstones, and sandstones, would act as plastic 

 materials. " If the rocks forming the cores of such ranges 

 as the Alps were crystalline before the upheaval of the 

 mountains, it is quite evident that, hard and rigid as they 

 were, they must have responded to the subterranean pres- 

 sures, and jlmood like lead through a die. In no other way 

 does it seem possible to account for the forms these cry.stal- 

 lino rocks have assumed." 



The uplift on this hypothesis throws the snporficial rocks 

 into a state of tension. Hence great superficial cracks. It 

 is from this cause, Mr. Reado thinks, that we find valleys of 

 denudation situated more frequently on anticlinals than 

 synclinals. Thus scarped faces are initiated. And he goes 

 so far as to say, that except in tlioso cases in which a scarped 



