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SCENERY OF SWITZERLAND. 
the ground. The character of the valley would de- 
pend greatly on the nature of the strata, being narrow 
where they were hard and tough; broader, on the 
contrary, where they were soft, so that they crumbled 
readily into the stream, or where they were easily 
split by the weather. Gradually the stream would 
eat into its bed until it reached a certain slope, the 
steepness of which would depend on the volume of 
water. The erosive action would then cease, but the 
weathering of the sides and consequent widening 
would continue, and the river would wander from 
one part of the valley to another, spreading the 
materials and forming a river plain. At length, as 
the rapidity still further diminished, it would no longer 
have sufficient power even to carry off the materials 
brought down. It would form therefore a cone or 
delta, and instead of wandering would tend to divide 
into different branches. 
When we look at some great valley of denuda- 
tion and the comparatively small river which flows 
through it, we may deem it almost impossible that 
so great an effect can be due to so small a cause. 
We find, however, every gradation from the little 
gully cut out by the last summer shower up to the 
great Canon of Colorado. We have to consider not 
only the flow of the water, but the lapse of time, 
