126 PHYSIOGRAPHY 



By the deposition of this river-borne material, the valleys below 

 glaciers are aggraded. The materials deposited by the glacial 

 streams are stratified, and so are in contrast with the drift left by 

 the ice itself. 



The gravel, sand, etc., deposited by a stream in the valley be- 

 low a glacier is a valley train. It is simply an alluvial plain devel- 



Fig. 133. Diagram to illustrate the profile of a valley train, and its relations 

 to the terminal moraine (m) in which it heads. 



oped by a stream flowing from a glacier, and carrying much gravel, 

 sand, etc. Valley trains are best developed just outside terminal 

 moraines (Fig. 133). 



In the case of an ice-cap, the water which issues from the ice 

 often fails to find a valley. Each issuing stream then tends to 

 develop an alluvial fan. By growth, these fans may unite, making 

 an alluvial plain, very much like a compound alluvial fan (p. 85). 

 Such a plain, composed of material washed out from the ice, is an 

 outwash plain (Fig. 134). Like valley trains, outwash plains are 

 best developed just outside the terminal moraines of ice-sheets, and 

 their materials are stratified. 



Lakes may exist at the ends or edges of glaciers, and drainage 

 from the ice may build deltas in them, just as other streams build 

 deltas in the standing water into which they flow. 



Streams sometimes exist in the ice (Fig. 1, PL XXXV, p. 128) 

 and under it. Streams under the ice (subglacial streams) in some 

 cases deposit gravel and sand in their channels, building them up, 

 so that when the ice melts the old bed of the stream appears as 

 a low but narrow ridge. Such a ridge is called an esker (Fig. 2, 

 PL XXXV). As water issues from beneath the ice, its velocity is 

 checked, and it sometimes makes extensive deposits of gravel and 

 sand at the margin of the ice. These deposits are stratified, but 

 the stratification is generally irregular. They are often made against 

 the edge of the ice, and when the edge melts they appear as mounds 

 and ridges, called kames (Fig. 135). 



As the ice melts away, the waters produced by the melting, flow 



