THE WORK OF SNOW AND ICE. 



307 



In the case of ice-sheets, too, in connection with which eskers are chiefly 

 developed, there is usually no surface material except at the immediate 

 edge, where the ice is thin and its layers upturned. 



At the mouths of ice-tunnels or ice-channels, especially where they 

 end against terminal moraines, sands and gravels are liable to be bunched 

 in quantity, giving rise, after the adjacent ice has melted, to pecuKar 

 hills and hollows of the knob-and-basin type. The hills and short 

 ridges are known as kames (see glacial period). Subglacial streams 

 may leave washed and assorted material in their tracks under the ice, 

 and this is sometimes buried under deposits made by the ice itself, so 

 that glacio-fluvial and glacial deposits are interbedded. 



Fig. 283. — Delta at Isola, Lake of Sils, Engadine, Switzerland. (Reid.) 



ICEBERGS. 



When glaciers advance into water, the depth of which approaches 

 their thickness, their ends are broken off (Fig. 284), and the detached 

 masses float away as icebergs (Fig. 285). Many of the bergs are over- 

 turned, or at least tilted, as they set sail. If this does not happen at 



