FEATURES OF GLACIAL LAKE HAMLINE. 193 



east accumulated the eastern moraine, and that on the west formed the 

 western moraine, at their respective margins. 



Glacial Lake Hamline. 

 extent and depth. 



Between these moraine belts a glacial lake was formed, held in on the 

 east by the ice filling and deeply covering the Mississippi valley in the 

 southeastern part of this city and for a considerable distance southward. 

 The length to which this lake grew is shown to have been at least ten 

 miles from south to north, and its maximum width was six miles or 

 more. Its depth, above the present bed of the Mississippi river was at 

 first about 250 feet; but this was reduced, probably by changes of the 

 places of outlet from the lake, as well as by erosion of its outlet chan- 

 nels, to about 185 feet when the latest of these plateaus was deposited. 



No shorelines of this lake have been recognized giving anywhere its 

 latest boundary after it ceased to be walled in by the ice on such parts 

 of its border, but I believe that its beaches may be found, by careful 

 search with leveling, on favorable gently sloping tracts of till south of 

 the river. It is known, however, that this entire lacustrine area was com- 

 paratively small, never comprising, perhaps, more than twenty-five square 

 miles, for its water level soon fell below the earlier plateau deposits. If 

 the ice border on the west retreated across the area of Minneapolis, and 

 to some undetermined distance up the Minnesota river valley, before the 

 ice barrier on the southeast was removed, the lake may have attained 

 a much larger area ; but no plateau drift nor other evidences of such 

 westward extension have been carefully observed. It will be very inter- 

 esting to extend a field examination w r est and south of Minneapolis with 

 this question especially in mind. 



MODIFIED DRIFT PLATEAUS FORMED IN LAKE HAMLINE 



While the first narrow avenue of glacial drainage extended northward, 

 enclosed by ice walls at each side, across the area of Saint Paul, the 

 Hamline and Como plateaus of modified drift were formed in this body 

 of water, which therefore may be appropriately named Lake Hamline. 

 Slightly later eastern tributaries of this lake deposited in the embayments 

 at their mouths the fourth and fifth plateaus, in their order, as here de- 

 scribed, and the series of the Summit Avenue, the sixth, and the smaller 

 eastern plateaus. 



OUTLETS TO RICH VALLEY. 



At the time of deposition of the six principal modified drift plateaus 

 the outlet of lake Hamline appears to have flowed across the first place 



