Mountain Chains. 49 



themselves according to their chemical affinities, and 

 distinct mineral materials were developed in layers from 

 elements that were in the original rock. 



I have stated that to produce this kind of meta- 

 morphism, heat aided by water is necessary, so as to allow 

 of internal movements in the rocks by the softening 

 of their materials, without which I do not see how 

 complete re-arrangement of matter accompanied by 

 crystallisation could take place ; and though it has 

 always been easy to form theories on the subject, yet 

 so little is known with precision about the interior of 

 the earth beyond a few thousand feet in depth, that 

 how to obtain the required heat is a difficulty. 



From astronomical considerations it is believed by 

 many persons that the earth has been condensed from a 

 nebulous fluid, and passing into an intensely heated 

 melted condition, by radiation into space at length 

 cooled so far, that consolidation commenced at the 

 surface, and by degrees that surface has gradually been 

 thickening and overlies a melted nucleus within. 



As the earth cooled and consequently gradually 

 shrunk in size, the hardened crust, in its efforts to 

 accommodate itself to the diminishing bulk of the 

 cooling mass within, became in places crumpled again 

 and again. Hence the upheaval of mountain chains and 

 disturbances of different dates, which have affected 

 strata of almost all geological ages. 1 



Reasoning on these disturbances, we know that strata 

 which were originally deposited horizontally have often 



1 This theory is not universally received, and has been variously 

 developed by different authors, but it would be quite beyond my 

 present purpose to discuss the subject in detail, and, as far as I know, 

 the hypothesis proposed by Elie de Beaumont seems best to explain 

 the phenomena exhibited by the outside of the earth. 



E 



