OLDER DRIFTS IN THE ST. CROIX REGION 543 



shale formations. The most common pebbles found in it are lime- 

 stones, granites, and greenstones. In its upper portion it gradually 

 becomes brown, passing into yellow-buff above. These brown and 

 buff portions are obviously merely the partially oxidized phases of 

 the drift which was originally nearly black in color. Upward the till 

 becomes less and less calcareous, due to leaching. The great amount 

 of calcareous and argillaceous material as well as the distinctive assem- 

 blage of crystalhne pebbles in this drift indicates that the ice which 

 deposited it came from the northwest and traversed the extensive 

 limestone and shale areas of Manitoba. It is an unmistakable 

 Keewatin drift. 



So far as could be determined, it appeared to be identical with 

 that great mass of bluish-black drift which makes up the bulk of 

 the strong moraine ridge through which the Northwestern Railroad 

 has cut its way, half a mile east of Hersey, Wis. This smooth ridge 

 of thickened drift near Hersey marks an eastern border of a great 

 Keewatin ice-sheet. Hersey is thirty-five miles southeast of the 

 St. Croix River at Osceola, and hence Osceola should be almost in 

 the line traveled by the Keewatin glacier which dumped Manitoban 

 material near Hersey. The age of this grayish-black drift has not 

 yet been conclusively estabhshed, but from what is known about it 

 at the present time and the relations elsewhere in Wisconsin, Minne- 

 sota, and Iowa, it would seem best to assign it tentatively to the Kan- 

 san. Whether a pre-Kansan drift of similar Keewatin character and 

 blackish color underlies it, as it does in some parts of Minnesota and 

 low^a, cannot yet be told. 



The partially oxidized upper portion of this drift-sheet has been 

 recognized in various portions of the St. Croix-Dalles quadrangle. 

 The wagon road which leads from the Osceola bridge to the Minne- 

 sota upland country exposes in descending order the following section 

 of older drift near the top of the river bank : 



Feet 



1. Wash material including much from the Wisconsin drift ... 4 



2. Gray-brown to yellow-brown calcareous till which breaks 



up into hard chunks 11 



3. Stratified sand, light-colored above and rusty-brown below 3J 



4. Dark-gray or bluish-gray till which is non-calcareous, ap- 

 parently having been leached 2 



5. Jordan sandstone. 



