10 BUREAU OF AMERICAN ETHNOLOGY [BULL. 33 



istic in the regions over which the glaciers extended. These forma 

 tions include especially the so-called glacial gravels which have 

 received particular attention at the hands of students of early a 

 man in this country. 



The several irregular ice invasions extended at their maximum as 

 far south on the Atlantic coast as Long Island. In the Delaware 

 valley they reached Easton, Pennsylvania; in the Ohio valley, Cin 

 cinnati, Ohio; and in the Missouri valley, the vicinity of St. Louis. 

 Beginning with the earliest subdivision, the several successive stages 

 of this period, with the few and uncertain chronological approxima 

 tions that have been made, are thus given by leading American 

 geologists : & 



Time in years since cli 

 max was reached 

 I. The Sub-Aftonian, or Jerseyan, the earliest knowil 



invasion (?) 



II. The Aftonian, the first known interglacial interval- (?) 

 III. The Kansan, or second invasion now recognized. 300, 000 to 1 , 020, 000 

 IV. The Yarmouth, or Buchanan, the second interglacial 



interval (?) 



V. The Illinoian, the third invasion 140, 000 to 540, 000 



VI. The Sangamon, the third interglacial interval (?) 



VII. The lowan, the fourth invasion GO, 000 to 300, 000 



VIII. The Peorian, the fourth interglacial interval (?) 



IX. The Earlier Wisconsin, the fifth invasion 40, 000 to 1 50, 000 



X. The fifth interval of deglaciation, as yet unnamed (?) 



XI. The Later Wisconsin, the sixth advance 20, 000 to GO, 000 



XII. The Glacio-Lacustrme substage. 

 XIII. The Champlain substage. 



The glacial invasion closed apparently with a gradual recession of 

 the ice, and thus terminated considerably earlier in southern than in 

 northern latitudes; this should be kept in mind in considering the 

 date of the ultimate disappearance of the ice in any limited region. 

 The precise date of the final recession of ice in any locality must 

 always remain in a large degree conjectural. The climax of the 

 final, or Champlain substage, in the latitude of the St. Lawrence 

 river, was apparently reached considerably more than ten thousand 

 years ago. 



Should it be assumed that man existed on the North American 

 continent before the present geological period, and taking into account 

 his osseous remains only, two important questions arise, namely, Avhere 



a The term early, as employed in this paper, applies only to the Pleistocene and older 

 geological periods. 



6 After Thomas C. Chamberlin and R. D. Salisbury s Geology, in, 383, 420, New York, 

 190G ; reversed in arrangement. See also Salisbury s The Glacial Geology of New Jersey, 

 Geological Survey of Nciv Jersey, v, Trenton, 1902. It should not be understood that all 

 of the given divisions apply to the entire vast glaciated area ; some of the terms relate 

 only to somewhat localized phases of the period. 



c A summary of the whole question of estimates by years is given in the chapter on 

 the Glacial period in volume in of Chamberlin and Salisbury s Geology. 



