LAKE AGASSIZ 53 I 



conspicuous and best known of all, and its sheets of till and drift 

 are far thicker than those of the other Glacial stages. Especially 

 conspicuous is the great terminal moraine which has been traced 

 almost across the continent. Beginning at Nantucket, the moraine 

 runs through Long Island and Staten Island to New Jersey, which 

 it crosses into Pennsylvania ; here it bends sharply to the north- 

 west to the boundary of New York, but turns southwest almost 

 at a right angle, reaching nearly to the Ohio River at Cincinnati. 

 It crosses in an irregular, sinuous line the states of Indiana, Illinois, 

 Iowa, and thence northwestward through the Dakotas and Montana 

 into Canada, where it probably reaches the Arctic Sea. 



In New England there is no clear evidence of more than one 

 Glacial stage. In part, this may be due to the later development 

 of the Laurentide glacier. The geologists of the Canadian Survey 

 believe that, " beginning at the west and going eastward, these 

 three great glaciers [i.e. the Cordilleran, Keewatin, and Laurentide] 

 reached their widest extent and retired in succession." (Tyrrell.) 



The final retreat of the ice was by slow stages with many halts. 

 In the central West are preserved many lines of moraine, with 

 kettle-holes, kames, and drumlins, which mark the successive 

 pauses in the retreat. 



An interesting episode of later Glacial times was the formation 

 in Minnesota and Manitoba of a great body of fresh water, Lake 

 Agassiz, which was 700 miles long from north to south. 



The great Keewatin glacier, which had long occupied the basin 

 of Lake Winnipeg and the Red River valley, began eventually to 

 retreat northward, while the Laurentide glacier, which, it would 

 seem, had begun to accumulate at a somewhat later date, gradually 

 advanced to the westward.' When the two sheets united, the 

 withdrawal of the Keewatin glacier had left nearly or quite all of 

 Manitoba free from ice. The junction of the Laurentide and 

 Keewatin glaciers formed a continuous ice-wall on the north and 

 east, shutting off the drainage, which seems before to have had a 

 free course to Hudson Bay, and damming back the waters into 

 a great lake. The lake rose until it overflowed southward into 

 the Mississippi by means of the now extinct Warren River. As 



