314 



DESTRUCTION OF MOUNTAINS. 



ing in numerous cascades to the lower valley. But the most power- 

 ful effects of these cataracts may be observed during thunder storms, 

 or after an unusually rapid thaw, when the upper rivulets overflow 

 their accustomed boundaries, and carry with them the loose stones 

 or masses of rock they meet in their descent, and dash them with in- " 

 conceivable violence into the lower waterfalls, breaking down the 

 solid rocks on each side, and deepening and enlarging the ravines 

 into which they fall. The operation of this cause will be again re- 

 ferred to in the following chapter. 



We need not indeed travel to the Alps to prove, that the mountains 

 have been, and are still wearing down. The rocky fragments in 

 Borrowdale ; the deep ravines made by torrents in the sides of 

 Skiddaw ; the immense blocks of granite torn from Wastdale Crag, 

 in Westmoreland, and scattered, many miles, over the adjacent coun- 

 ties offer striking proofs of this. The central parts of England 

 had once, a greater elevation than at present ; pebbles, formed 

 of the Charnwood Forest rocks, are spread all over the midland 

 counties. Masses of the rocks of Cumberland and Wales, more 

 or less water-worn, occur almost every where under the alluvial plains • 

 of Cheshire and Lancashire. Beds of flint gravel, formed by dis- 

 integration of chalk rocks in which flints were imbedded, occur in 

 many parts of England at a considerable distance from the sea, or 

 from the chalk districts. 



The transportation of these masses of rock, or beds of stones 

 and gravel, cannot have been effected by any thing like the present 

 action of rivers in England, and is generally referred to the more ex- 

 tensive operation of deluges, during great convulsions of the globe ; 

 but if we return to the Alps, and view {he effects now taking place, 

 we must admit, that it is not always easy to make the distinction 

 between alluvial and diluvial depositions. 



Innumerable blocks of granite and other primary rocks, torn from 

 the fcentral range of the Alps, are scattered over the calcareous 

 mountains, at a great distance from this range, or are spread in heaps 

 in many of the distant valleys. All of the great rivers that issue 

 from the Alps, where the valleys open into the plains, have made 

 deep sections in beds composed of the ruins of the mountains, and 

 exhibit proofs of the vast destruction that has taken place. The river 

 Doire, where it enters the plains of Piedmont, has cut through a 

 mass of fragments more than 1500 feet in depth; these fragments 

 consist of irregular blocks of granite, mica slate, and serpentine, fre- 

 quently more than thirty cubic yards in extent, covered by smaller 

 fragments, and by earthy matter from the decomposition of the softer • 

 rocks ; the fragments decrease in s'ze as their distance increases 

 from the parent mountain. 



Whoever has ascended the lofty eminences immediately below the 

 highest pinnacles of the Alps, can scarcely fail to have received sen- 

 sible proofs, of the daily and hourly disintegration of the mountains. 



