626 W. A. JOHNSTON 



fronts of the two glaciers to the north and northeast and the high ground to 

 the south and west. Thus Lake Agassiz had its beginning. Its waters 

 rapidly rose until they overflowed southward into the valley of the Mississippi 

 and then gradually declined as River Warren deepened its channel. 1 



By his more recent work in the region lying to the south of 

 Hudson Bay, Tyrrell has shown that the last invasion of glacial 

 ice in that region was by an ice sheet which advanced in a south- 

 westerly direction and overlapped a portion of the area previously 

 occupied by an ice sheet which he named the Patrician Glacier. 

 This last advance of the ice extended in a southwesterly direction 

 at least as far as the headwaters of the Severn River and in a 

 westerly direction approximately as far as the Hayes River, where 

 it was met by a readvance of the Keewatin glacier. 2 



Field work done by the writer during portions of the seasons 

 of 1913 and 1914 in the vicinity of the Rainy River and Lake of 

 the Woods, Ontario, has brought forth evidence which confirms 

 Tyrrell's view that Lake Agassiz had at first a rising stage, due to 

 the blocking of the northward drainage, and later subsided, and 

 that, during the entire existence of the lake, the ice border was far 

 to the north and northeast. This conception of the life-history of 

 Lake Agassiz differs radically from that of Warren Upham, by 

 whose work Lake Agassiz is best known, and whose interpretation 

 has been most widely accepted. The object of the present paper 

 is to present the evidence which confirms Tyrrell's view as to the 

 genesis of Lake Agassiz and to point out that the acceptance of this 

 view has an important bearing upon the question of the character 

 and cause of the epeirogenic movements which deformed the shore 

 lines of Lake Agassiz. 



upham's conception of the life-history of lake agassiz 



Glacial Lake Agassiz is best known from the work of Warren 

 Upham, the results of which were published in 1895 by the United 

 States Geological Survey as Monograph 25. Upham's field work 

 in connection with the investigation of the basin of Lake Agassiz 

 was done some thirty years ago and was largely confined to the 



1 J. B. Tyrrell, "The Genesis of Lake Agassiz," Jour. Geo!., TV i,i$q6), S13. 



2 J. B. Tyrrell, "The Patrician Glacier South of Hudson Bay." Congres Geologique 

 International, Canada, icjij. Cornpte-Rendu (Ottawa, Canada. 1914), pp. 523-34. 



