' GLACIAL DRIFTS IN MINNESOTA 
387 
simply explained in a historical account of progress in finding 
crucial evidence relating to the drifts generally of Minnesota. 
It appears that, in the extreme southeast corner of Minnesota, 
three glaciers, each carrying “gray” drift, came in succession, and 
that each stopped short of the full extent of the previous one. 
On top of each of these three glacial sheets there, peat beds are 
found, so as to prove interglacial and post-Glacial time and con¬ 
ditions — the peat being local and occurring where one sheet over- 
lies another. This is essentially the view taken of that part of the 
field by N. H. Winchell ^ and there is still no evidence to disprove 
his interpretation of it. 
Winchell had found Houston County (No.T, PI. xxxiv), free 
from bouldery drift, and likewise much of Winona County (No. 
2) ; but Fillmore County (No. 3) had a belt of drift patches, or 
thinly scattered drift, across the greater part of it, while the “great 
drift sheet,” or thick drift (Kansan), was found at the west end 
of the County. The thin drift patches in Fillmore County (No. 
3) “present the appearance of greater age than the drift of the 
western portion of the county,” as Winchell thought, and he found 
further that peat beds there and in lower Mower County (No. 5) 
lie under the thicker “old” drift, and on the eroded surface of 
the thin “older” drift sheet. There need be no doubt that where 
peat beds divide the drift, as is often found in wells of that re¬ 
gion, the “older” is the Nebraskan, and the “old” is the Kansan 
of later parlance, but the thin scattered border drift is made into 
a special problem. 
At the time of Chamberlin and Salisbury’s description of the 
Driftless Area,^ the problem in Minnesota of distinguishing the 
Pleistocene Glacial drift from debris of other formations at the 
surface was found to be simple in its solution. Greenstones, quart¬ 
zites, and quartz, in large pebbles and boulders were easily recog¬ 
nized as not coming from the local limestones and sandstones of 
southeast Minnesota. Such stones belonged to the Drift. Cer¬ 
tain small pebbles of that kind might in fact belong to the stream- 
deposited gravels of the Cretacic age that lie on the uplands, but the 
large pebbles and boulders were there as evidence of glaciers. 
With criteria of this kind, the authors mentioned found in south- 
1 Minnesota Geol. and Nat. Hist. Surv., Vol. I, pp, 311-313, 1884. 
2 Sixth Ann. Rep., U. S. Geol. Surv., pp. 205-322, 1885. 
