GLACIAL INVESTIGATION IN MINNESOTA IN 1911 733 



Moines Valley, but which also extended southeastward across the portion of 

 the Mesabi Range west from Hibbing, Minnesota, and spread to the left and 

 right in a basin which divides its drainage between the Saint Louis and Mis- 

 sissippi Rivers. This ice-movement deposited the so-called "gray drift" of the 

 Minnesota Reports. It forms only a thin veneer on the ix)rtions of the Leaf 

 Hills and Fergus Falls moraines which it overrode, and it failed to cover all 

 of the Leaf Hills moraine. The correlative position of the Lake Superior Lobe 

 is found to have been but little beyond the western end of the present lake, in 

 Carleton County, Minnesota. A large glacial drainage line opened a great 

 valley along the Saint Louis between Floodwood and Carleton, but was there 

 turned southwestward because of the presence of the Superior lobe. The rela- 

 tions of this latest ice-movement from central Canada to the Glacial Lake 

 Agassiz are such as to make necessary a radically different intei'i)retation 

 from that given by TTpham in his monograph on Lake Agassiz. 



Discussion 



Mr. J. B. T\'RRELL said : Mr. Leverett's paper can not but be of interest to 

 every student of glacial geologj^ in America, and especially to those who have 

 been working in Canada, where the three great centers of ice-dispersion are 

 located from which the ice traveled .southward into the United States, for he 

 has shown another point of connection between the Keewatin Glacier to the 

 west and the Labradorean glacier to the east, through a large drainage chan- 

 nel from the former to the latter. 



The presence of this drainage channel would appear to show clearly that the 

 southern lobe of the Keewatin Glacier was of the same age as the Superior 

 lobe of the Labradorean glacier, but I do not see why this should modify very 

 materiallj^ the explanation of the formation of Lake Agassiz as given first by 

 Mr. Warren Upham and afterwards somewhat modified by myself.^ 



It is quite probable that this lake had its beginning when the latest stage 

 of the Keewatin Glacier began to retire northward, and it is possible that the 

 water followed this glacier northward as far as the northern boundary of 

 Minnesota, but it is also quite clear that as the Keewatin Glacier retired 

 northward the Labradorean glacier advanced from the east into the basin of 

 Lake Winnipeg, in many places as far as its western shore, though at this 

 time it does not appear to have crossed the strip of land between Lakes 

 Winnipeg and Manitoba, or to have reached the Manitoba escarpment to the 

 west of the latter lake, but it terminated in a moraine which is now repre- 

 sented by islands in Lake Winnipeg and points on its western shore. 



For greater definiteness this line of islands and stony points may l>e called 

 "The Winnipeg moraine." This Winnipeg moraine was then the western or 

 southwestern, termination of the Labradorean glacier in its last advance into 

 Manitoba. There is no question whatever about its existence and about the 

 manner of its formation. The striae of the Labradorean glacier are general 

 on the rocks down the east shore of Lake Winnipeg, where they have been 

 beautifully preserved by the overlying covering of lacustrine clays deposited 

 on the floor of Lake Agassiz. In some few places the earlier stria' of the Kt^- 

 watin (Jlacier have been preserved in depressions in the rock surface, which 



-J. B. Tyrrell: The Genesis of Lake Agassiz. Journal of Gcologv. vol, 4. 1800, pp. 

 811-815. 



