22 THE ILLINOIS GLACIAL LOBE. 



were three main centers of dispersion aside from Greenland. The Cordil- 

 leran region of western Canada contained one ice field from which there 

 was dispersion in all directions. The province of Keewatin, west of Hudson 

 Bay, contained another ice field which spread in all directions and reached 

 the glacial boundary in Missouri and States to the southwest. The third 

 ice field occupied the highlands east and south of Hudson Bay. It spread 

 to the borders of the Atlantic on the north and east, and to the borders of 

 the Mississippi and Ohio on the southwest and south. The two ice fields 

 bordering Hudson Bay probably for a time coalesced to form the Lauren- 

 tide ice sheet of Dawson. 1 But they were apparently distinct and inde- 

 pendent centers for a considerable part of the Glacial period. The names 

 Keewatin and Labrador seem appropriate for these independent centers of 

 glaciation, the former being a name proposed by Mr. Tyrrell, and the latter 

 one which has been used by several glacialists in correspondence and to 

 some extent in print. The name Cordilleran has been applied by Dawson 

 to the ice field in western Canada. There appears to have been less com- 

 plete coalescence of this ice field with the Keewatin than that between the 

 Keewatin and Labrador ice fields. 



The Cordilleran ice field, as shown by Dawson, occupied a portion of 

 the Rocky Mountains and extended eastward into the province of Alberta, 

 in the early stage of glaciation, when the Albertan drift sheet was 

 deposited. 2 This advance long preceded the maximum westward extension 

 of the Keewatin ice field. Whether the sub-Aftonian or any other 

 deposits of the Keewatin ice sheet are as old as the Albertan, as noted 

 above, is not satisfactorily determined. 



The Keewatin ice sheet apparently reached its farthest limits on the 

 borders of the Mississippi at the Kansan stage of glaciation. The recogni- 

 tion of the sub-Aftonian — an older deposit than the Kansan — in southern 

 Iowa is based upon the exposures of this drift sheet under a somewhat 

 fresher sheet of Kansan drift. The extent of the sub-Aftonian toward the 

 south and west compared with that of the Kansan is not yet determined. 

 In a paper presented at the twelfth annual meeting of the Iowa Academy 

 of Sciences, in December, 1897, Dr. H. Foster Bain, of the Iowa Geolog- 

 ical Survey, gave a careful review of the features of the sub-Aftonian and 



1 See Am. Geologist, Vol. VI, 1890, pp. 153-161. 



2 Bull. Geol. Soc. America, Vol. VII, pp. 31-66; issued November, 1895. 



