Nearly 30 years ago it was discovered that in the early Pleistocene the master stream of the southeastern South Dakota region followed the valley of lames River to its present mouth and then the Missouri below, and also that the present course of the Missouri above Yankton was outlined around the edge of the great ice-sheet as late as the Wisconsin stage.
Later studies made in preparing the Elk Point folio led the writer to the conclusion that there had been an earlier advance of the ice-sheet down the James River Valley at a time when the drainage level was about 300 feet higher than at present. Whether this was during the Kansan stage or the Iowan stage has not been determined, but probably it was during the Kansan. At that stage the Dakota lobe extended as far south as West Point, Nebraska, and the drainage from the . . .