BULLETIN'OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 5, pp. 87-100 January 18, i894 



THE SUCCESSION OF PLEISTOCENE FORMATIONS IN THE 

 MISSISSIPPI AND NELSON RIVER BASINS 



BY WARREN UPHAM 



(Read before the Society August 16, 1893) 



CONTENTS 



Page 



Introduction 87 



The Lafayette Formation and the Saskatchewan Gravels 89 



Glacial Drift and marginal Moraines 92 



Loess and other Modified Drift Deposits 94 



Lake Agassiz and its Deltas 96 



Preglacial epeirogenic Elevation 96 



Depression of the Land previous to the maximum Stage of the Glaciation 97 



Re-elevation during the Departure of the Ice-sheet 98 



Estimates of the Duration of the Quaternary Era 99 



Discussion 100 



Introduction. 



During fourteen years, since June 9, 1879, my field observations and 

 constant studies, successively for the geological surveys of Minnesota 

 and of the United States, have been directed chiefly to the glacial and 

 modified drift of Minnesota, northern, central and northwestern Iowa, 

 the eastern borders of Soutli Dakota, nearly all of North Dakota, except- 

 ing the country southwest of the Missouri river, and the large prairie 

 portion of Manitoba. These areas comprise the upper part of the Mis- 

 sissippi basin, the whole district drained by the Red river of the North 

 above the city of Winnipeg, and the lower part of the basin of its large 

 western tributary, the Assiniboine, the two last named streams being 

 portions of the Nelson river system, sending their waters through lake 

 Winnipeg and the Nelson to Hudson bay. 



In mapping the marginal moraines of the Minnesota and Iowa lobe 

 of the ice-sheet, the first and outermost, named the Altamont moraine, 

 was found to extend in a [J-shaped loop south to Des Moines. Ten later 



XII-Bur.L. Geot,. Soc. Am., Voi,. 5, 1893. (87) 



