Seminar Details

Seminar Lab Date: November 24, 2025

Seminar Lab Subject: The Rock Elm Meteor Impact Structure, Pierce County, WI: Discovery and Basic Geology (V)

Seminar Lab Presenter: Bill Cordua, Ph.D., Geology Emeritus, University of Wisconsin River Falls

Seminar Lab Location:

Virtual lecture 7:00 PM CT.

Participation instructions will be e-mailed to GSM members. If you are not a member of GSM and wish to attend this free seminar online, register as follows by 8 AM CT Monday, Nov 24: Go to the Contact menu above and select “Ask GSM”. In the form that appears, enter your name and e-mail address. Enter “Nov 24 lecture” in the subject line. In the message body, please enter the city and state or country from which you will view the seminar. You will receive instructions by e-mail prior to the lecture. Check your spam folder if the instructions do not appear in your in-box at least one hour prior to the lecture.

Seminar Lab Detail:

Summary: The Rock Elm structure has been recognized as a geological anomaly for well over a century, attracting prospectors, charlatans and scientists. It is interpreted as formed by an extraterrestrial impact during the middle Ordovician 430-505 Ma. Both gold and diamonds are found in unusual quantities in the alluvium of streams draining the feature. The talk will outline its basic geological features, review the evidence for its interpretation as an impact structure, speculate why gold and diamonds are associated with it and relate it to similar features in the Midwest.

Biography: Dr. Bill Cordua is a retired professor from the University of Wisconsin – River Falls where he taught geology for 40 years. He has published many technical articles and written over 100 articles for the general public on geology. Dr. Cordua is in the education division of the Rockhound and Lapidary Hall of Fame and has received the Katherine Greacen Nelson Award honoring those who have made outstanding contributions to the earth sciences in Wisconsin.