THE PLEISTOCENE OR GLACIAL PERIOD 871 



ice sometimes seems to have lost vigorous motion, and drainage 

 along its sides gave rise to deposits of stratified drift which, after 

 the melting of the ice, had somewhat the form of terraces, while 

 their slopes and upper surfaces had something of the topography 

 of kames. Such terraces have been called kame terraces 1 (Fig. 581). 

 Kame terraces are of frequent occurrence in the glaciated part of 

 the Appalachian Mountains. 



2. Beyond the edge of the ice. When the waters issuing from 

 the ice found themselves in valleys, they aggraded their valleys 

 in many cases, developing valley trains, 2 which often extended far 

 beyond the unstratified drift with which they were contempora- 

 neous. Valley trains are usually associated with stout terminal 

 moraines (Fig. 230 p. 272). 



Where the water escaping from the ice spread over a plain in- 

 stead of being concentrated in valleys, the deposits took on a form 



Fig. 581. Diagram to illustrate kame terraces. ABC represents the strat- 

 ified drift of the kame terraces which are underlain by ground moraine. 

 Till also covers the valley bottom. 



more like that of alluvial fans. By union, these fans often became 

 extensive, making outwash plains (also called overwash plains, 

 moraine plains, frontal aprons, etc.). When the water issuing 

 from the ice flowed into standing water it tended to develop deltas. 

 Many such deltas are known about extinct lakes, and about the 

 borders of existing lakes, the levels of which have been lowered. 



3. Beneath the ice. Subglacial streams seem sometimes to 

 have deposited gravel and sand in their channels. Where such 

 streams were confined to definite channels, and where their courses 

 remained constant in position for a long time, the channel deposits 

 stood out as ridges after the melting of the ice. Such ridges of 

 gravel and sand are eskers (Fig. 231). It is not to be inferred that 

 eskers never originated in other ways, but it seems clear that the 

 aggradation of the channels of subglacial streams is the principal 



1 Salisbury, op. cit., pp. 156 and 121-124 respectively. 



2 3d Ann. Kept., U. S. Geol. Surv., and Jour. Geol., Vol. I. p. 534. 



