184 
SCENERY OF SWITZERLAND. 
which will be described in the next chapter. River 
terraces have no relation to the rock and follow the 
slope of the river, while weather terraces follow the 
lines of the strata. 
This consideration throws light on the cases in 
which a river valley expands and contracts, perhaps 
several times in succession. 
We often, as we ascend a river, after passing 
along a comparatively flat plain, find ourselves in a 
narrow defile, down which the water rushes in an 
impetuous torrent, but at the summit of which, to 
