(Wloun^aitt Ba^te 



Avalanches of snow often pile upon them, bury- 

 ing them deeply. 



Gravity and water are filling with debris and 

 sediment these basins which the glaciers dug. 

 Many lakes have long since faded from the 

 landscape. The earthy surface as it emerges 

 above the water is in time overspread with a 

 carpet of plushy sedge or grass, a tangle of wil- 

 low, a grove of aspen, or a forest of pine or 

 spruce. The rapidity of this filling is dependent 

 on a number of things, — the situation of the 

 lake, the stability of the watershed, its relation 

 to forests, slopes, meadows, and other lakes, 

 which may intercept a part of the down-coming 

 sediment or wreckage. This filling material 

 may be deposited evenly over the bottom, the 

 lake steadily becoming shallower, though main- 

 taining its original size, with its edge clean until 

 the last; or it may be heaped at one end or piled 

 along one side. In some lakes the entering 

 stream builds a slowly extending delta, which 

 in time gains the surface and extends over the 

 entire basin. In other lakes a side stream may 

 form an expanding dry delta which the grass, 



i6i 



