This study deals with the stratigraphy, landforms, and history of the drift that covers an area of 5,800 square miles in southwestern Manitoba and southeastern Saskatchewan. The area, which is bounded by Latitudes 50 and 51 degrees N and by Longitudes 100 and 102 degrees W, is part of the Interior Plains Region.

A stratigraphie succession is proposed for the Riding Mountain area. From oldest to youngest it is informally named the Ancient Drift, Lower Drift, Minnedosa Drift, and Upper Drift. This succession includes four principal tills separated by intertill sediments. The three youngest tills crop out in one locality designated as the 'reference section'. The two lowermost tills are here separated by a stratified silt containing grass that yielded a radiocarbon age of more than 31,000 years B.P., and bones of the ground squirrel Citellus and the large vole Microtus. Some of the differences in the physical properties of the exposed tills can be recognized by means of carbonate content determinations, stone counts, stone orientation measurements, and grain size analyses. The Ancient Drift was encountered only in deep boreholes. The Lower Drift and Minnedosa Drift have a fairly wide distribution within the map-area as suggested by the cuttings and electric logs from some 30 boreholes.

The landforms within the map-area include various types of moraines, outwash plains, lake plalns, kames and eskers. An extensive belt of hummocky stagnation moraine covers the highest part of the area. Glacio.fluvial and glacio-lacustrine deposits within the hummocky stagnation moraine are topographically identical to the latter.

The last major glacier advance was from the northwest. During final deglaciation the Riding Mountain Upland was covered by stagnant ice while active ice lobes remained over the adjacent lowlands. Glacial meltwater was damned by this active ice and formed extensive lakes over the stagnant ice on the Upland. As deglaciation continued these lakes were finally drained by channels that formed in front of, on top of, and beneath the ice lobes.

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