244 
SCENERY OF SWITZERLAND. 
such curve as that in Fig. 47, from the source to its 
entrance into the sea. 
The existence of a hard ridge would not give 
rise to a Lake, it would delay the excavation of the 
valley; above it the slope would become very gentle, 
but no actual basin could be formed; we should have 
some such section as in Fig. 67. The action of a 
glacier is different; it picks out as it were the softer 
Fig. 67. — Diagram to illustrate the action of rivers and glaciers. 
A, A', Hard ridges; B, B‘, B", Softer strata; C, C, Slope of running 
water; D, D, Slope of ice. 
places, and under similar circumstances basins might 
be formed above the harder ridges as shown in the 
dotted lines, D, D. 
In many of the Swiss valleys the pressure of the 
ice on its bed must have been very great. The 
Rhone glacier not only occupied the basin of the 
Lake of Geneva, but rose on the Jura to a height of 
950 metres. The lake is 309 metres deep, so that 
the total thickness of ice must have been over 
