162 



ON THE OBIGIN OP MOUNTAIN EANGES. 



followed by an equivalent uplift, if referred to the soa-level." 

 Has it, I would ask, been followed by subsidence proportional 

 to the consequent lowering of the isogeotherms ? 



The more I consider what must bo the effects of subse- 

 quent contraction, the more difficult do I find it to accept 

 Mr. Mellard Beade's hypothesis. Relying partly on his 

 experiments on a small scale with lead, he tells us that the 

 materials laterally ridged up by expansion cannot be drawn 

 back again daring contraction. Hence there remains a 

 permanent total uplift in the range. " None of the material 

 of the earth laterally displaced by expansion can be di-awn 

 back by tension, as is the case with metal plates ; conse- 

 quently the elevation," he adds, " is more rapid and effec- 

 tive." But the subsequent contraction must take place 

 somewhere. I am ready to admit, and have indeed for many 

 years been in the habit of teaching, that whereas reversed 

 faults are due to intense lateral pressure, normal faults are 

 the result of local and comparatively superficial contraction, 

 and involve a lengthening of the area in which they occur. 

 But I do not think that in any known area of the earth's 

 surface there is evidence of so groat an amount of local 

 contraction as is necessitated by the after-tensions involved 

 in Mr. Mellard Keado's hypothesis. 



For many reasons therefore I feel constrained to reject 

 Mr. Mellard Reade's views, gladly as I welcome his volume, as 

 presenting an adequate account of the phenomena of moun- 

 tain building ; and as a minor criticism, I would question his 

 view of the plasticity of solid granite or gneiss. The analogy 

 of the flow of metals will not help us hero. I rather incline 

 to the view that the gneiss, which exhibits in the Alps the 

 well-known fan structure, was, during the throes of mountain 

 upheaval, in an imperfectly solid condition thi'ougU incipient 

 aqueo-igneous fusion. 



