GLACIAL FEATURES OF ST. CROIX DALLES REGION 239 



during the last glacial epoch, was due to the work of glaciers from 

 the Labrador ice-cap. But over a large part of Minnesota the sur- 

 face drift dates from an invasion of the Kewatin ice-sheet from the 

 northwest. The Labrador ice arrived first, covering much of Min- 

 nesota; subsequently its deposits were buried by the advance from 

 the northwest. The eastern limit of the Kewatin invasion was 

 reached near the St. Croix River, in the vicinity of the Dalles. 



The St. Croix Dalles quadrangle comprises those portions of Polk 

 County, Wis., and Chisago County, Minn., which border on the 

 St. Croix River between latitude 45 15' and 45 30', and longitude 

 92 30' to 9 2 45'. The river, with some windings, flows generally 

 south through the western half of the quadrangle. On opposite 

 banks are the centrally located towns of Taylor's Falls and St. 

 Croix Falls, while seven miles downstream is Osceola, Wis. The 

 region as a whole is covered with a thick mantle of drift, which 

 effectually hides the rock formations, except where uncovered by 

 the river, or where an occasional boss of Keweenawan trap pro- 

 trudes with a roche moutonneed surface. 



There are not only two separate drift-sheets represented as sur- 

 face formations in different parts of the quadrangle, with the like- 

 lihood of an older till below, but the two dissimilar drifts both belong 

 to the Late Wisconsin. The Dalles region is peculiar in having 

 the eastern half of the quadrangle glaciated by the Labrador ice- 

 sheet, and the surface of the western part covered by till from the 

 Kewatin sheet. The glacier from the former source was the first 

 to appear as a vigorous sheet, spreading heavy deposits of drift over 

 the entire area. First to come, it was the first to go. It had retired 

 quite beyond this region before the weaker development from the 

 Kewatin gathering ground, spread to the St. Croix River. This 

 ice crossed into Wisconsin less than a mile at St. Croix Falls, though 

 about four miles in the vicinity of Osceola; but it quickly withdrew, 

 leaving in most places only a thin covering of Kewatin drift. To 

 get an idea of the work and relative importance of the two ice-sheets, 

 conceive of the glacier of the red drift, or the Superior (Labrador) 

 glacier, as a vigorous, long-enduring sheet, which produced most 

 of the present topography, and of the glacier of the gray drift, or the 

 Kewatin glacier, as a thin, transient advance of ice, which left as 

 its record only a gray veneering of the red hills. 



