THE BERNESE OBEKLAND. 
143 
river, and the rocks on both sides are identical; it 
corresponds to no difference of geological structure. 
The valley of the Rhone is, on the contrary, a 
“geotectonic” valley, due to a great fold in the 
strata, but still geologically speaking of but recent 
origin. The great Bernese Oberland wall (Fig. 121) 
is an escarpment due to the weathering back of the 
Jurassic strata; and the valley of Leuk, like that of 
the Reuss, is a transverse valley of erosion. 
Though the Aar massif is detached, it is no 
isolated phenomenon. The Protogine, which forms its 
nucleus, is mineralogically and chemically very similar 
to that of Mont Blanc, and it is obvious that these 
two mountain masses are merely two upthrows of the 
same central rock. 
Atmospheric influences and the agency of water 
have cut the slopes of the longitudinal ridges into 
deep valleys, thus forming transverse ridges, which 
again are carved by denudation into separate sum- 
mits. 
These ridges, therefore, form N.W. and S.E. 
chains, as for instance on the west of the massif, the 
ridge which runs from the Bietschhorn to the Dubi- 
horn, or from the Nesthorn to the Faschhorn and 
the Gredetschhorn; and on the east from the Schreck- 
horn and Lauteraarhorn. 
