392 
GLACIAL DRIFTS IN MINNESOTA 
wide, and the hills covered by the clays of well weathered rock 
formations. 
From its place of beginning and along all of its course, the 
glacier had presumably clays rather than sands or gravels to 
displace before the bed-rock was scratched. Residuary pebbles 
and boulders, of course, existed locally to be picked up by the 
ice as it moved forward, but since residuary clays act more nearly 
as a lubricant rather than as an abrasive, it may be imagined that 
the Nebraskan glacier slipped along relatively easily, over a 
clay ground moraine in which were few stones. This glacier 
carried clay, mainly. Since also a clay moraine is much more mild 
in its surface features than a stony moraine is, as we see from 
comparison of the Kewatin and Patrician drifts of the Wisconsin 
stage in Minnesota now, the Nebraskan moraines of re-advance 
would be even that much more low-lying — scarcely moraine-like 
at all — even when they were fresh. Under such conditions, out- 
wash of laminated clays rather than of gravels also filled the 
valley bottoms both during advancement and recession of the 
glacial front-wall. Valleys that were traversed lengthwise could 
be plowed free of clays, but those lying tranverse might be plas¬ 
tered over more or less, in the advance. 
Nebraskan till, in fact, closely resembles alluvium, with tree- 
trunks, clay-polished pebbles and boulders, and a minor amount 
of fresh rock materials of all kinds. Now as to whether this 
was spread as a continuous sheet of till, or was in patches, largely 
with bare-rock areas between, is not known, but the scarcity of re¬ 
maining patches to the north in Minnesota may be taken as an 
indication that Minnesota was denuded rather than covered, while 
Iowa and also southeast Minnesota was more thickly drifted. 
Whatever was here, however, had been reduced to remnants by 
erosion before the next glacier came. What is found now are 
the sparse patches in the belt bordering the Driftless Area, till 
under the Kansan drift on uplands, as in Mower county, at 1300 
feet above sea-level, and filling of pre-Glacial ravines as that 
at Mankato at 800 feet elevation,—all too few to prove more 
than that a great Nebraskan glacier was here, and that a great 
erosion interval separated it from the Kansan drift. 
The Kansan drift in Minnesota is all of Kewatin origin and is 
