CHAPTER VIII. 



BEACHES FORMED WHEN LAKE AGASSIZ OUTFLOWED 

 NORTHEASTWARD. 



Fourteen shore-lines of Lake Agassiz have been traced, with determi- 

 uation of their heights, through portions of their extent, which lie below 

 the McCauleyville beaches and were formed after the lake ceased to outflow 

 southward. The River Warren, no longer receiving the drainage from the 

 melting ice-sheet and from the rainfall of the vast basin of Lake Agassiz, 

 was suddenly reduced, when the lake obtained a lower northeastern outlet, 

 to the much smaller IVIinnesota River; and the alluvium of this stream 

 formed a Avatershed between Lakes Traverse and Big Stone, partially filling 

 the former channel of outflow from the glacial lake. Chapter V has already 

 considered the courses of the successive new avenues of outflow to the 

 northeast, probably at first flowing back southward along the border of 

 the retreating ice-sheet, and thus passing through tlie great Laurentian 

 lakes to the Mississippi, and later to the Hudson. Though the courses of 

 the northeastward outlets remain unexplored, the beaches inarking the 

 stages of Lake Agassiz while tributary to them are found to be separated 

 only by vertical intervals varying from 10 or 15 to 45 feet tlu-ough all the 

 time of its reduction from the level of Lake Traverse and the McCauley- 

 ville beaches to Lake Winnipeg. On the latitude of the south end of Lake 

 Winnipeg the fall of the surface of the glacial lake during this time was 

 about 280 feet, Lake Winnipeg having stood at first above its present 

 height and liaving been since lowered 20 feet by the erosion of the Nelson 

 River. 



The three highest shore-lines on the area from which the lake receded 

 during its northeastwai-d drainage are named the Blanchard beaches, and 

 the next five in descending order the Hillsboro, the two Emerado, and the 

 two Ojata beaches, from towns on or near their course in North Dakota. 



