36 MOUNTAIN AND MOORLAND 



land, and that long winding ridges or embankments of 

 gravel called " eskers," very characteristic of Sweden, 

 appear to mark the courses of ancient sub-glacial 

 rivers. 



The second great kind of mountain is known as 

 folded, and is formed by some sort of crumpling of the 

 earth's crust. They are also called Deformation moun- 

 tains. Most of the great chains and ranges of moun- 

 tains belong to this group of Folded or Fold moun- 

 tains, and they differ in character according to the way 

 in which the crumpling occurs. No one has ever seen 

 this kind of mountain in the making, but there is 

 evidence that some were formed all at once by one 

 continuous and probably very slow crumpling, and 

 that others were formed by a succession of lateral 

 thrusts interrupted by long periods of rest. If we 

 take a piece of thick felt, like that used for a crumb- 

 cloth, and compress it from the sides, we can make a 

 series of folds or ridges which mimic in a rough way 

 simple mountain ranges, especially if the felt is satu- 

 rated with water on a cold winter day and freezes hard 

 while we hold it tight. If we press the felt unequally 

 the folding will be more complicated ; if it is not of the 

 same texture throughout fresh complications will 

 arise ; if the felt is made of several different layers of 

 different ages and materials there may be further 

 intricacies in the folding ; and, finally, if the crumpled, 

 layered, and hard-frozen felt be partly thawed and then 

 compressed very hard so that the folds break in places 

 and under layers are thrust above upper layers, and 

 so on, we may begin to get an idea a far too simple 

 idea, of course of what has happened in the formation 

 of complex Fold mountains like the Alps. 



