Rock Talk
By Larry Harred
Rocks, fault lines, mines,
and meteors: Our RFArea REA meeting on
March 8, 2018, featured a presentation by Dr. William Cordua on western
Wisconsin’s wild geology.
Dr. Cordua began his talk by
telling his audience that geology is everywhere—even in Wisconsin—and offered
some interesting local examples. After
presenting a general geological history of Wisconsin, illustrating the
chronology with a map of glacial drift coverage and a chart of rock formations,
Dr. Cordua discussed this “layer cake” of rocks in more detail, moving from the
deepest and most ancient, the Cambrian Sandstone, to the shallowest and most
recent, the Platteville and Decorah formations.
With maps, photos, and other
illustrations, Dr. Cordua told the stories of four sites of geologic interest
in western Wisconsin. If you drive along
Hanley Road near Hudson, you can observe the first: the results of the geologic
upheaval that occurs along major fault lines.
The second is nearby, in Knapp.
The Knapp Gold Mine, active from 1920 through 1925, uncovered the
precious metal that had been deposited by glacial drift. Panning for gold in the area may still net a
person small particles of “flour gold.” The iron mined in the late 19th
and early 20th centuries at the third site, the Gilman Iron Mine,
was deposited in a similar manner. And
finally, though it is hard to spot from the ground, the nearly perfect circle
of the Rock Elm Disturbance is easily visible on satellite imagery. This feature is in fact the impact crater
left by a large meteor.
Dr. Cordua ended the
presentation by answering questions about a variety of subjects, from
geologists’ methods to the diamonds of Plum City.
Dr. Cordua earned his
undergraduate degree from George Washington University and his M.A. and Ph.D.
from Indiana University. He joined the
geology faculty at UW-River Falls in 1973 and retired in 2012. He is a member of the Wisconsin Geological
Science Hall of Fame and has won an award from the Museum of Geology/Earth
Science in Oshkosh, WI.
