142 V ALLEY-S IN ANTICLINAL FOLDS. 



unlike these valleys of erosion, owe their existence, directly or in- 

 directly, to elevatory forces ; hence they are called valleys of eleva- 

 tion. When the rocks are compressed so as to be thrown into parallel 

 folds such as form the Jura Mountains and some other chains, then the 

 small synclinal depressions between the mountains constitute valleys. 

 In our own country the rocks have been too long exposed to denud- 

 ing agencies, and too little contorted in times comparatively recent for 

 examples of valleys of this kind to have remained unchanged. But 

 many of the undulations of chalk scenery have been produced as a 

 consequence of small undulations of the underlying rock. Valleys 

 formed by contortion are nowhere more grandly exhibited than in 

 the Western Territories of North America, where the rocks are thrown 

 into multitudinous parallel elevations with intervening valleys. 1 



Anticlinal Valleys. But when folds of this kind are formed 

 beneath the sea, and rise slowly from out of it, the tops of the folds 

 are broken away, because the rocks are stretched and cracked and planed 

 down; and then atmospheric agencies complete the work of hollow- 

 ing out a valley where a hill once had been. Not entirely, perhaps, 

 in one geological age, but during immense periods of time, most of the 

 upward folds in Wales and in many parts of the world have been 

 excavated into deep valleys. The part of the country which had 

 originally been a valley produced by elevation, comes to withstand 

 denudation better, in consequence of the hardness imparted to its con- 

 stituent rocks by compression, often thus forming the loftiest moun- 

 tain peaks. Such synclinal folds are Snowdon and Moel Hebog. 

 The valleys around such mountains, at their first compression, rose 

 to immensely greater heights. It is like an illustration of the Scrip- 

 tural teaching that " Every valley shall be exalted, and every hill 

 made low." The valleys are innumerable which were formed in this 

 way. Some of the broadest are the Bristol Channel, and probably 

 both ends of the English Channel. In countries formed of old and 

 contorted rocks, as many valleys have been produced by elevation, as 

 have been excavated by erosion in countries formed of newer rocks. 



Valleys have existed for all geological time, but it is not often 

 that they have survived the changes of the earth's surface so that we 

 can recognise their former extension. A few such examples, however, 

 will come under our notice of ancient valleys excavated in the moun- 

 tain limestone of the North of England, and afterwards filled up by 

 the Trias, again to be partially cleared out by existing streams. And 

 similarly among the Austrian Alps we shall find at Gosau and near 

 Salzburg many valleys excavated in the Triassic rocks, in which Cre- 

 taceous strata have been deposited, in their turn to be laid bare by 

 ravines cutting through them. 



1 Hay den, Reports U.S. Geog. and Geol. Survey of the Territories. 



