THE GENESIS OF LAKE AGASSIZ 631 



clays overlie and in the eastern portion of the district also underlie 

 the calcareous till, with which they are closely associated. In some 

 sections there is a sort of transition upward from the unstratified 

 till into the laminated clays; that is, in the lower portion of the 

 clays distinct laminae of clay are separated by unstratified stony 

 material resembling the underlying till. The stony layers at the 

 base rarely exceed a few inches or at most a foot in thickness and 

 rapidly die out, so that "the transition beds" are, as a rule, only 

 4 or 5 feet thick. The laminated clays in the district range in 

 altitude from 1,060 up to at least 1,200 feet, but they are generally 

 only a few feet in thickness. These clays were deposited in a glacial 

 marginal lake which is here referred to as Early Lake Agassiz. 

 This lake was associated with an advance of the Keewatin glacier 

 which deposited the calcareous till in the region. The clays were 

 in part deposited during the time of advance of the ice sheet, for 

 in places till overlies the clays. This relation is well seen in the 

 sections exposed in the gravel pit one and one-half miles west of 

 Fort Frances, where 8 feet of calcareous till overlie laminated 

 clays, which are again underlain by non-calcareous, fmvio-glacial 

 sands and gravels. The laminated clays were also in part deposited 

 during the time of retreat of the ice. Early Lake Agassiz was, 

 however, largely if not wholly drained before the later Lake Agassiz 

 came into existence, for the desposits of Lake Agassiz rest uncon- 

 formably on the calcareous till and on the closely related laminated 

 clays. 



Deposits of Lake Agassiz. — Numerous raised beaches of Lake 

 Agassiz occur in the district, at altitudes ranging from 1,100 to 

 1,200 feet. The strongest and best-developed beach extends north- 

 ward for some distance from the vicinity of the town of Rainy 

 River. The altitude of this beach near the town of Rainy River is 

 1,117 f eet - Ten miles northeast of this locality its altitude is about 

 1,125, and twenty-four miles northeast its altitude is about 1,140. 

 Higher beaches occur at various altitudes up to at least 1,200 feet. 

 A comparatively small part of the drift-covered area lying between 

 Rainy Lake and Lake of the Woods rises more than 1,200 feet, but 

 in the northern portion of Minnesota immediately south of Rainy 

 River district drift-covered areas rise considerably higher. In this 



