GLACIAL OR ICE-LAID DEPOSITS 



45 



The material carried and pushed along by the ice is usually very 

 irregularly distributed, giving the glaciated areas an undulating 

 to rolling topography. The ridge formed at the terminus of the 

 glacier is the terminal moraine (Fig. 3(>). It usually presents 

 a steep outward slope with a very gradual inward slope. The 

 surface of the moraine is rolling, billowy, or has " rounded knob and 

 basin" topography. The height of moraines may vary from a few 

 feet to several hundred, while the width may be from a half mile 

 to ten miles or more. Recessions and advances of the glacier may 

 build up new moraines or override old ones, tearing them down 

 completely or transforming the material into lenticular hills, called 

 drumlinx (Figs. 37 and 3S), whose longer axis i< in the direction 

 of movement of the latest ice sheet. 



Super- and subglacial streams formed hills of gravel and sand 

 called kam.es, or ridges of the same material called eskers (Figs. 30 

 and 40). 



Fia. 40. The material composing Adeline csker consists of coarse sand and gravel. 

 The ledge is conglomerate formed by cementing the mind and gravel with carbonate of lime. 

 (R. W. Dickenson.) 



The Glacial Period. The three centers of accumulation in 

 North America during the glacial period were the Labradorean in 

 Labrador, the Keewatin immediately west of Hudson Hay, and the 

 Cordilleran in the Kooky Mountains of Canada. These centers cov- 

 ered large areas (Fig. I',*), and ice movement started from these in 

 practically all directions, but probably not from all centers at the 

 same time, or at least not to the same extent. Smaller centers of ae- 



