290 THE BEAUTIES OF NATURE chap. 



downhill. He imagined tliat the downward 

 slope had a fall of about 40 or 50 feet per- 

 pendicular. We here have unequivocal evi- 

 dence that a ridge had been uplifted right 

 across the old bed of a stream. From the 

 moment the river course was thus arched, 

 the water must necessarily have been thrown 

 back, and a new channel formed. Prom that 

 moment also the neighbouring plain must 

 have lost its fertilising stream, and become 

 a desert." ^ 



The strata, moreover, often — indeed gener- 

 ally, as we have seen, for instance, in the case 

 of Switzerland — bear evidence of most vio- 

 lent contortions, and even where the convul- 

 sions were less extreme, the valleys thus 

 resulting are sometimes complicated by the 

 existence of older valleys formed under pre- 

 vious conditions. 



In the Alps then the present configuration 

 of the surface is mainly the result of denuda- 

 tion. If we look at a map of Switzerland 

 we can trace but little relation between the 

 river courses and the mountain chains. 



I Darwin's Voyage of a Naturalist. 



