Page 17

PECULJARITIES OF THE FOX RIVER
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to a level only slightly above Lake Winnebago (747 ft.) on the
plain. Alden interprets this as evidence of a late stage of the
Green Bay lobe, whose extent is now shown by the loop of red
moraine within which the red till of the Lake Winnebago region
is included. This lobe represents a very late and relatively
short period of re-advance of the Green Bay ice tongue, following
the accumulation of the red clay in the Lake Winnebago lowland.
The red clay extends westward in the Fox River Valley as far as
Berlin, and northward as far as Shawano, and down the Valley
of the Lower Fox to Green Bay. This peculiar red deposit is
not confined to the region under discussion, but also occurs
along the Wisconsin shore of Lake Michigan from Milwaukee
northward, and along the south shore of Lake Superior.
CAUSE OF THE LARGER LAKE
Remembering that the entire Fox River-Lake Winnebago
basin is a lowland, enclosed by higher land on all sides except for a
narrow opening at the north end, it is easy to understand that if
anything should obstruct this opening, the northward drainage of
the entire basin would be blocked, and a lake would be produced.
This is evidently what occurred when the Green Bay lobe of the
glacier pushed its way into the valley from the north. The ice
itself acted as a dam, not a fixed one, but a slowly advancing or
receding one, and as the ice lobe pushed slowly up the valley,
the lake became smaller and smaller and finally disappeared
entirely as the glacier spread over the whole basin and beyond.
Long afterward, as the Glacial Period was coming to a close and
the glacial ice was melting, the ice front melted back toward the
north and the Green Bay lobe again became a dam acros the
Fox River Valley, and again produced a lake in the Fox River-
Lake Winnebago lowland. Still later, when the glacier had
entirely withdrawn from Wisconsin, and the ice dam had melted
away, the glacial lake, whose waters had been flowing westward
into the Wisconsin River, now drained northward by the Fox
River and the lake shrank to about its present size. Why the
lake was not entirely drained has already been explained (p. 15).
CHARACTERISTICS OF THE LOWER Fox RIVER
As the Upper Fox is noted for its extremely slight fall (4 inches
to the mile), so the Lower Fox is notable for its rapid fall, and
especially for the fall in a nine-mile stretch between the Grand
Chute (Appleton) and the Grand Kaukauna. A profile of the
river is shown in Plate VIII.
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