ON MR. M. READe's WORK ON MOUNTAIN BUILDINO. 65 



rise, forced up under the influence of heat expansion in a 

 more or less plastic state, hence the ridging, folding, and 

 overthrow, which are features of all great mountain chains. 

 Besides this, the archsean rock, being more heated and 

 possessing greater expansive strains than the overlying 

 sedimentaries, must break through them, showing itself in 

 the higher peaks, while the sedimentary strata rest on the 

 lower flanks. 



These considerations imply that the initial upheaval of 

 our great range has been geologically rapid, After this 

 we have abundant evidence of variation in subterranean 

 activity, each pause and each renewal of activity adding to 

 the complexity of the phenomena ; but where movement 

 has been once initiated, there it seems to continue. The 

 Pyrenees afford an interesting example of this. Kaised first 

 in early Palaeozoic times, then depressed for a long period, 

 after that subjected to two more great movements and 

 three of lesser importance, for seven in all participated in 

 the formation of this great range. The Himalayas afford 

 another instance of similar alternate and prolonged action. 

 Now, if the formation of these ranges was due chiefly to 

 secular contraction, though we should expect pauses in 

 the process, yet there should be no depression — whatever 

 action there was must force the mountains upwards, as it 

 compressed the area on which they stand. But if the forma- 

 tion of the mountains is due to altered conditions of the 

 subjacent magma, then this elevation and depression is in 

 harmony with our theory. 



Another important point. On the theory of secular con- 

 traction, those parts of a district which lie on either side 

 of a mountain range must travel over several miles in their 

 approach to each other. American geologists state that 

 abundant evidence of such translation exists. Taking the 



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