Sunday, March 25, 2018

RFAreaREA Meeting--March 8, 2018--Rock Talk


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.