EFFECTS OF THE MOVEMENTS OF WATER 37 



season as liquid. But in those colder ancient days the 

 accumulation of ice in polar regions was much greater. 

 Slowly a great sheet of ice crept southward over the land, 

 ironing the surface as it went. It picked up huge masses 

 of earth and boulders and carried them along. Miles deep 



FIG. 15. Photograph showing a terminal moraine of coarse boulders deposited at 

 the front of a glacier. 



the ice accumulated in the north, and it flowed to the south 

 (see Fig. 14). The southern edge of the great ice-field 

 changed with the seasons, and changed as the climate 

 changed. In summer it melted back faster than it flowed 

 forward. In winter it regained the lost ground. Always, 

 as it melted, it kept depositing ridges and sheets of rock 

 and soil. Finally, the climate changed so much that this 

 ice-sheet was melted far back to the north, where it now 

 remains, covering Greenland and other regions. But the 



