548 ROLLIN T. CHAMBERLIN 



the contact with the overlying red till. Some cuts show a distinct 

 erosion unconformity between the two drift-sheets. 



At the present state of knowledge, the following drift-sheets have 

 been recognized in the St. Croix-Dalles region: 



1. A thin surface mantle of gray Wisconsin drift deposited by a 

 glacier from the Keewatin center, as described in previous papers. 



2. An upper red drift deposited by a glacier of Wisconsin age from 

 Labrador, as similarly described. 



3. A sheet of brownish-red to carmine-red sandy drift left by an 

 ice-invasion coming from the Labrador center across the Lake 

 Superior basin and extending as far to the south as the moraine at 

 Hampton, Minn.; age consistent with Illinoian. 



4. A sheet of dark grayish-black, calcareous, clayey till deposited 

 by a vigorous advance of ice from the Keewatin gathering-ground 

 and extending as far to the southeast as Hersey, Wis.; age probably 

 Kansan, but still open to question. 



I 



