SCENERY OF SWITZERLAND. 
I98 
forests, for instance, in a lateral valley will consider- 
ably increase the erosive power of the stream, and 
the amount of material brought down. Rocks which 
yield readily to the action of weather and water will 
naturally supply most material, and give rise to the 
largest cones, especially if they form hard pebbles. 
On the other hand, the Flysch, which, as a rule, 
exeicises little resistance, does not produce such im- 
portant cones as might be expected, because it dis- 
integrates into fine particles which are easily washed 
away. The Cargneule, on the contrary, produces 
large cones, because it breaks up readily, but into 
hard pieces. 
Such cones sometimes raise the bed of the valley 
and dam back the water, and thus form a marshy 
and unhealthy tract. Thus in the Upper Valais be- 
low Oberwald is a succession of such cones, one suc- 
ceeding another, and with more or less marshy 
ground between them. At Munster there is a fine 
cone, and further down are many others at intervals. 
The two largest are those of the Illgraben at Leuk, 
and the Chamoson at the mouth of the Losentze, 
both of which raise the level of the valley above 
several feet. That of the Borgne (Fig. 51), near 
Sion, drives the river to the foot of the opposite 
mountain. 
