* 
104 = W. Upham—Minnesota Valley in the Ice Age. 
“ART. XV.—The Minnesota Valley in the Ice Age; by 
WA HAM. 
| 
[Concluded from page 42.] 
Two principal glacial epochs can be especially distinguished, 
each subdivided by times of extensive recession and re-advance 
of the ice,*us shown by features of the drift in this State. In 
the first Glacial epoch, when the ice attained its greatest area, 
all of Minnesota except its southeast corner was deeply covered 
by the continental ice-sheet, and its border was several hundred 
miles south of this district, in Nebraska, Kansas, Missouri and 
southern Illinois, Indiana and Ohio, extending somewhat. be- 
yond the Missouri River, but terminating north of the Ohio 
River, except in the vicinity of Cincinnati, where it reached a 
short distance across that river into Kentucky, as recently 
proved by Professor Wright. In the later very severely cold 
epoch, the ice-fields were of less extent, and terminated in the. 
central part of the United States from 50 to 800 miles within 
their earlier limit, covering all the basin of the Minnesota river, 
but not enveloping a large tract in the southwest corner of Min- 
nesota and leaving uncovered a much larger area than before 
in the southeast part of the State. The terminal moraines, 
which form conspicuous belts of rolling and hilly drift in Wis- 
consin, Minnesota, Iowa and Dakota, were accumulated in the 
boundaries of the ice of the last glacial epoch. Between these 
epochs the ice was melted away within the basins of the Min- 
nesota and Red Rivers, and probably from the entire State. 
The greater part of the till appears to have been deposited by 
the earlier ice-sheet; and during its retreat this till was over- 
spread in some places, especially along the avenues of drainage, 
by beds of modified drift, or stratified gravel, sand, and clay, 
_ washed from the material that had been contained in the ice 
_ and now became exposed upon its surface to the multitude of 
rills, rivulets and rivers, that were formed by its melting. 
In the principal interglacial epoch, this drift-sheet was chan- — 
nelled by water-courses until its valleys were apparently as nu- 
merous and deep as those of our present streams. The inter- 
glacial drainage sometimes went in a different direction from 
that now taken by the creeks and rivers; and the valleys then 
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excavated in the drift, though partly refilled with till during oe 
the last Glacial epoch, are still, in some instances, clearly marked 
by series of lakes, as in Martin County, in the south edge of 
Minnesota. More commonly the interglacial water-courses must 
have occupied nearly the same place with the valleys of the 
present time; and there seems to be conclusive proof that this ~ 
was true of the entire valley of the Minnesota River. Along 
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