94 



PHYSIOGRAPHY 



pletely, and the debris is spread less widely. In form, the delta 

 differs from the alluvial fan in that its edge has a steep slope (corn- 



Fig. 98. A delta in a lake. The village is Silva Plana, in the Engadine, 

 Switzerland. (Robin.) 



pare Figs. 102 and 103). A delta begins below water, but it is soon 

 built up to the water-level, and even above it. That part of the 

 delta above the surface of the water in which it is built is like a flat 

 alluvial fan. 



Fig. 99. A general view of the lower part of the delta of the Mississippi. 



Waves, currents, etc., may prevent the building of a delta, but 

 otherwise all sediment-bearing streams make deltas where they 



