110 THE GLACIAL LAKE AGASSIZ. 



THE CONTINENTAL, ICE-SHEET.' 



The relation of Lake Agassiz to the ice-sheet leads us to inquire more 

 particularly what were its l)oundaries, area, and thickness, its centers of 

 outflow, the manner of its final departure, and the areas probably occupied 

 by its latest remnants. 



Boundaries. — The extreme southern limit of the glacial drift and of the 

 ice-sheet during its greatest extent, and the division between the earher 

 drift, belonging to the Kansan and East lowan stages of the Glacial 

 period, and the later drift, Ijelonging to its East Wisconsin stage, during 

 which Lake Agassiz existed, have been delineated by Professor Cham- 

 berlin,^ and are again here presented in PI. XVI, combining the results 

 obtained by many observers during the past twenty-five years. The 

 southern margin of the drift and of the maximum ice extension is shown 

 to lie wholly within the United States, excepting that it is indented at the 

 eastern foot of the Rocky Mountain range by an angle which barely 

 touches the forty-ninth parallel. Dr. Dawson's recent map of the extent 

 of the drift in the western part of Canada, however, places the apex of this 

 angle south of the international boundary, along which he has had 

 exceptional opportunity for examination.^ But the limit of the ice-sheet in 

 the Wisconsin stage, or the time of formation of the outermost prominent 

 moraines, is found north of this boundary from the one hundred and fourth 

 to the one hundred and fourteenth meridian; that is, across southern 

 Assiniboia and Alberta, from the Coteau du Missouri to the Rocky 

 Mountains. The abundance of lakelets held in hollows of the drift and 

 the small amount of change in the drift contour since the departure of 

 the ice-sheet indicate that during its time of accumulation of marginal 

 moraines in these provinces it reached south to the Wood Mountain and 

 Cypress Hills and to Lake Pakowki and the upper portion of Milk River. 



"The greater part of this discussion of the extent and thickness of tlie ice-sheet is from the 

 author's previously published articles, "Glacial Lakes in Canada," Bulletin, G. S. A., Vol. II, 1891, pp. 

 243-274; and "(iliiciation of Mountains in New England and New York," Appalachia, Vol. V, 1889, pp. 

 291-312 (also in the Am. Geologist, Vol. IV, Sept. and Oct., 1889). 



»U. S. Geol. Survey, Seventh Annual Report, PI. VIII. The Great Ice Age, third edition, 1894, 

 PI. XV. 



sTrans. Roval Society of Canada. Vol. XUl. sec. 4. 1890, PI. II. 



