I 1 8 SCENERY OF SWITZERLAND. 
was a lake down to, geologically speaking, a very 
recent period. 
The bottom of the valley to a considerable depth 
consists of alluvium containing freshwater and some- 
times land shells. The Navisance has cut 300 to 
400 feet through gravel. 
On both sides of the Valais, marks of glacial 
action reach to a great height, and the upper limits 
of the ancient glacier can often be clearly traced. 
The glacial deposits in the lateral valleys are also of 
immense magnitude. The valley of Devens, between 
the Grionne and the Avan50n, is especially remark- 
able in this respect, and contains many immense 
blocks. 
On the left bank of the Rhone a great moraine, 
which has been rendered classic by the labours and 
descriptions of Charpentier, extends, with some in- 
tervals, from the plateau of Verossaz above St. Maurice 
by Monthey to Muraz. It is almost entirely composed 
of Protogine from the north slopes of the Mont Blanc 
range. Some of the blocks are so large that they 
have received special names— the Pierre a Dzo, Pierre 
a Muguet, etc. 
At Bex are the celebrated Salt mines in the 
Trias which have been worked for over 200 years, 
