194 
SCENERY OF SWITZERLAND. 
Third Stage. 
Finally, when the inclination becomes too small 
the stream cannot carry farther the stones and mud 
which it has brought down, and spreads them out 
in the form of a fan, forming a more or less flat 
cone or delta — a cone if in air, a delta if under 
water; and the greater the volume of water, the 
gentler will the slope be, so that in great rivers it 
becomes almost imperceptible. At this part of its 
course, the stream instead of meandering, will tend 
to divide into several branches. 
Cones and deltas are often spoken of as if they 
were identical. The surface and slope are indeed 
similar, but the structure of a delta formed under 
water (see p. 186) is by no means the same as that 
of a cone formed in the air. 
Deltas have generally a very slight inclination, so 
far as the surface is concerned, while the layers be- 
low stand at a greater inclination. Most of the Swiss 
Lakes are being gradually filled up by the deposits 
of rivers. The Lake of Geneva once extended far 
up the Rhone Valley to St. Maurice if not to Brieg. 
It presents also a very typical delta at the mouth of 
the Dranse near Thonon. Between Vevey and 
Villeneuve are several such promontories, each 
