IOWA ACADEMY OP SCIENCE 
245 
drift observed is not the typical Kansan and may be Wisconsin, but 
most of the exposures studied, are apparently Kansan. On the basis of 
the drift alone, onie would not separate the areas, but the conclusive 
evidence is the topography, and along with this, the absence: of a. loess- 
covering over the Dakota plain, the presence of boulders on the surface 
and the questionable drift of the region agree. 
Southeast of Shindlar, along the Chicago, Rock Island and Pacific 
Railway as it descends to the Big Sioux valley, there are a number of 
drift cuts. The plain above is Wisconsin but the drift exposures are 
Kansan with the possible exception of the first cut southeast of Shindlar, 
which comes at the very edge of the plain just as the descent begins. 
In this cut, there is a loose, sandy drift near the surface, which breaks 
out in rounded fragments and crumbles to a sandy mealy clay when 
crushed in the hand. It grades downward however to a. harder, more 
plastic clay, which breaks with the more definite Kansan fracture. 
Just south of the northwest cornier of section 36 of Sioux Falls town- 
ship (T. 101 N., R. 49 W.), a yellowish-brown, sandy drift comes to the 
surface, except for a thin covering of soil. This is just inside the Wis- 
consin area and good glacial topography continues off to the southeast. 
In passing only a half mile to the west, the Wisconsin boundary has 
been crossed and a loess covering of 4 to 6 feet overlies the Kansas drift 
(Fig. 3). 
At the northeast corner of section 10, township 100 north, range 50 
west, just outside the Wisconsin margin, there are several cuts of loess, 
one 12 feet deep, and some of them show Kansan drift below the loess. 
About 80 rods to the south', a road cut shows, at the surface, a brownish- 
grey drift with considerable sandy material and occasional pebble 
bands. Passing down the slope, through a vertical thickness of 8 feet, 
the drift is found to rest upon a brownish-yellow loess deposit, several 
feet in thickness, the base of which is not exposed. This is apparently 
a case where the Wisconsin ice near its margin pushed over some loess 
without tearing it, up and mixing the material with its drift. 
Is the failure of the Wisconsin drift-sheet real or only apparent? 
We are accustomed to think of the drifts of different, ice-epochs as 
presenting each its own characteristic lithological features, but if two 
ice-sheets advanced over the same route and eroded the same rock forma- 
tions, there is little reason why the drifts should differ. The Wisconsin 
drift was obtained from the same rocks as the Kansan drift, or is in 
large part simply reworked Kansan drift, so that we should not ex- 
pect the drifts to be distinctly different. However it is not believed 
that any large amount of the drift exposed in the deeper cuts, as along 
