274 



GEOLOGY 



streams usually have high gradients, swift currents, and smooth 

 bottoms, and hence give little opportunity for lodgment. Further- 

 more, ice-sheets, in connection with which eskers are chiefly de- 



Fig. 232. The end of a glacier in Spitzbergen. (Rabot.) 



veloped, usually have 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, and in the re-entrant angles 



Fig. 233. An iceberg. (Robin.) 



of the edge of the ice, sands and gravels are liable to bo bum-hod in 

 quantity, giving rise, after the adjacent ico has melted, to peculiar 

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

 ridges of stratified drift formed in this way aro known as 



