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Whitbeck, R. H., 1871-1939 (Ray Hughes) / The geography and economic development of southeastern Wisconsin

Chapter II. Physical features and climate of southeastern Wisconsin,   pp. 5-23 PDF (4.8 MB)

Page 5

The region with which this bulletin deals is a small part of
the great central valley of the United States-an extensive
plain most of which belongs to the basin of the Mississippi, but
a small part of which is included in the drainage basin of the
Great Lakes. The rain falling upon eastern Wisconsin finds
its way both to the Gulf of Mexico and to the Gulf of St.
DEPOSITION OF SEDIMENTS. The land of southeastern Wiscon-
sin shares with the rest of the central plain of the United States
a geological history that reaches far back into the past. More
than once the waters of the sea have covered this plain, at
times joining the Gulf of Mexico to the Arctic Ocean. For a
part of the time at least they were warm waters, as revealed
by the fact that colonies of coral-building polyps built extensive
coral reefs which now make up parts of the limestone of eastern
WVisconsin. The region was covered by the sea for an enor-
lmlous length of time, as is indicated, for example, by a sand-
stone formation which is nearly a thousand feet thick; and a
limestone formation which was probably built up very slowly,
that is 300 or 400 feet thick. The evidence is conclusive that
this corner of Wisconsin, like the region for hundreds of miles
around, was under the sea and was receiving sediments brought
from the land by streams for a very long period of time.
UpLIFT. Later, an uplift of this sea bottom occurred and
the upper beds of sand and limy material-compacted into
rock-were raised hundreds of feet above sea level and became
part of the continent of North America. The great interior
sea, which connected the Gulf with the Arctic Ocean, was forced
to recede, and land took its place. But the uplift was relatively
gentle, for the rocks still lie in nearly horizontal beds. This
uplift took place a very long time ago, and a large proportion
of the uppermost beds has been weathered and eroded away.

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