Origin of V alleys. 291 



evident when we consider that many such basins are sepa- 

 rated by precipitous depressions only, similar to terrace-like 

 declivities, where there has been a perfect absence of any 

 dams for the collection or restraint of water. 



In the longitudinal valleys, on reaching which the Alpine 

 streamshave already lost much of their force, considerable beds 

 of gravel occur (p. 212), which have been cut through by the 

 rivers. Here again, river erosion always appears of slight im- 

 portance in relation to the extent of these valleys. At the 

 terminal gap-like openings of these valleys the eroding power 

 of the streams is abundantly perceptible ; but we can scarcely 

 dare to attribute the cutting through of these rocks to such 

 a cause. The signs of erosion reach at the highest to some 

 100 feet (French), whilst the rock walls are many thousand 

 feet high. It is remarked (p. 219) that the distinguished 

 observers, L. von Buch, F. Hoffmann, 0. d'Halloy, E. de 

 Beaumont, Thurmann, B. Studer, and others, have indeed 

 proved in different regions of the earth, that the formation of 

 valleys is not effected by casual erosion, but is most inti- 

 mately connected with the causes that gave rise to the general 

 configuration of a district. In relation to this are especially 

 to be regarded the manifold windings of valleys, the great 

 change in their direction and extent ; whereas in mere erosion, 

 water would have taken the shortest and straightest passage. 

 It frequently happens also, that a valley cuts through a moun- 

 tain crest; whilst on the other hand, running water would have 

 taken an easier, and frequently already opened, course to one 

 side. Hoffmann has proved this particularly by the well 

 known Porta We stphalica in the Weserthal; Omalins d'Halloy 

 cites very similar phenomena in the course of the Rhone. 



The author considers, therefore, that although running 

 water and atmospheric influences effect important changes on 

 the earth's surface, yet these operations have not been suffi- 

 cient to give rise to the extensive series of Alpine valleys. 



The real causes of the origin of these valleys appear to lie 

 in a series of successive elevations, associated with certain 

 sinkings. The great basins found at the extremities of the 

 valleys and in their wider developments, and repeated on a 

 smaller scale on the declivities of the mountains, seem es- 

 pecially to point to a contraction and expansion (zuruck 



t2 



