﻿276 Canadian Record of Science. 



inap-maker. But only in this way can a basis be obtained 

 from which it is possible to decide upon the causes of the 

 formation of mountains. 



The force concerned in this work seems to be principally 

 a contraction of the outer crust of the earth, connected 

 with a shortening of the diameter caused by the gradual 

 cooling of our planet. 



We observe two phenomena through which the con- 

 traction is evident : either horizontal movement — that is, 

 folding ; or vertical contraction — that is, subsidence. 



According to the predominance of one or other of these 

 two movements, we see the surface of the earth laid out in 

 long folds, as in the Alps and the Ural ; or we have flat 

 table-lands, as in the Sahara and Central Eussia, or lines 

 of subsidence, as in the Dead Sea, or whole regions 

 depressed, as on the western side of the Apennines. 



The folds of the mountain rancres run in loner lines 

 forming curves and often abut against older fragments by 

 which they are turned aside from their course. They 

 bend like the waves on a disturbed surface of water, and 

 the outer folds which form the edge of the range are 

 sometimes completely overturned, so that along these 

 edges the strata of the folded rocks are met with in 

 reversed order. Thus parts of the surface of the earth 

 appear here as table-lands, there as areas of depression, 

 and in still other places as folded and overturned portions 

 of the crust, in which, as already stated, the more recent 

 foldings have been restricted in their development by the 

 already existing structure of the country. 



From this it is, however, seen that the relief of the 

 earth's surface does not by any means always correspond 

 with the deeper structure. Therefore, in order to obtain 

 a correct understanding of the facts, the structure, that is, 

 the lines of folding or the lines of fault, must be kept 

 in view. These lines are the determinants, not the relief. 



Take, for instance, the Hartz. According to contour. 



