no REVIEWS 



Keewatin and Laurentide ice-sheets, alternating in their advance and 

 retreat. 



A lobe of the Keewatin ice-sheet first invaded this region from the 

 northwest and extended into Iowa and to western Wisconsin. This 

 lobe formed the Kansan drift in Minnesota and the Kansan and pre- 

 Kansan drift further south. Glacial Lake Grantsburg was formed in 

 the upper Saint Croix valley, and for a time had its outlet northward 

 into Lake Superior. The retreat of this ice was followed by a marked 

 interglacial period. 



The second great ice invasion, the lowan, came from the northeast. 

 The Rainy Lake and Lake Superior lobes of the Laurentide ice-sheet 

 extended to western Minnesota, and the latter lobe was deflected 

 southward into Iowa. This ice does not appear to have retreated far 

 beyond the limits of Minnesota, and was followed in this region by a 

 comparatively short interglacial period. 



During the third invasion, the Wisconsin, the Minnesota lobe of 

 the Keewatin ice-sheet again advanced from the northwest across 

 central Minnesota into Iowa. At the same time the lobes from the 

 Laurentide ice-sheet advanced southwestward until they reached the 

 northeastern limit of the Minnesota lobe. The final retreat of the three 

 lobes was contemporaneous, forming glacial lakes and numerous 

 moraines. The Keewatin ice-lobe appears to have completely retired 

 from Minnesota slightly before the lobes of the Laurentide ice. 



A new mapping of the moraines formed by the various lobes 

 during their final retreat is presented m support of the view? advanced. 



The movements of the several lobes of the Laurentide ice-sheet 

 present a combination not noticed heretofore. The lobes from Green 

 Bay and Lake Michigan eastward over the Great Lakes show three 

 well-defined advances — the Illinoian, lowan, and Wisconsin. The 

 Chippewa, Lake Superior, and Rainy Lake lobes show two advances, 

 the lowan and Wisconsin. The western lobes in Canada, north of 

 Minnesota, show only one advance, the Wisconsin. 



It appears that the advance of the northern part of the ice-sheet 

 to the west was much slower than the advance to the south, and the 

 time required for the Laurentide ice-sheet to reach Lake Winnipeg 

 was sufficiently long to allow of two and three advances and retreats 

 in other portions of the ice-sheet. 



