222 THE GLACIAL LAKE AGASSIZ. 



these pass near Blanchard, N. Dak., and thence are denominated the 

 Bhmchard beaches. Tlie next in descending- order is the Hillsboro beach, 

 the succeeding two are the Emerado beaches, and the two next lower the 

 Ojata beaches, named similarly from other towns of this State. The 

 remaining- six lower beaches are named from localities in Manitoba. In 

 the same descending order, they comprise the Gladstone, Burnside, Ossowa, 

 Stonewall, and Niverville beaches, the last being- double. There are thus 

 in total thirtv-one separate shore-lines of this lake in the northern portion 

 of its area explored h\ me ; and all of them, excepting the lowest, extend 

 south of the international boundary. 



DEPENDENCE OF THE LAKE EEVEES ON THE EROSION AND 

 CHANGES OF OUTLETS. 



PROGRESS OF EROSION BY THE RIVER WARREN 



Thi'ough the greater part of the duration of Lake Agassiz its outlet 

 remained constantly in one position, and the stream of its overflow, named 

 the River Warren, eroded during that time the remarkable valley, rather to 

 be described as a trough-like channel, mostly 1 to 2 miles wide and 150 

 to 230 feet deep, which is now occupied by Lakes Traverse and Big Stone 

 and the Minnesota River. There is evidence, however, in the terraces of 

 modified drift along the Slinnesota Valley, that in large part its erosion 

 was eifected in preglacial time and during stages of retreat and readvance 

 of the ice-sheet previous to its final departure, when it was the barrier of 

 this glacial lake. ^ The general surface of the moderately undulating drift 

 sheet, having swells 10 to 25 feet above its hollows, which stretches away 

 on each side from the top of the blufts inclosing- this valley at Lakes 

 Traverse and Big Stone, is about 1,100 feet above the sea, and the heights 

 of these lakes at then- low stage of water are, respectively, 970 and 962 

 feet. Before the retreat of the ice uncovei'ed this tract, a channel 40 or 

 50 feet deep probably existed liere, nearly or quite continuous, along the 

 course that was taken bj^ the Ri^•er Warren in its first discharg-e from 

 the incipient Lake Agassiz ; for this level, much below the even expanse 



' "The Minnesota VaUey in the Ice age," Proc, A. A. A. S., Vol. XXXII, for 1883, pp. 213-231. 

 Geology of Minnesota, Vols. I and II. 



