Abstract

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 South Dakota, nearly all of North Dakota, excepting the country southwest of the Missouri river, and the large prairie portion of Manitoba. These areas comprise the upper part of the Mississippi 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 . . .

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