Glacial Erratics: Strange Rocks from Stranger Times
September 30 @ 6:00 PM – 7:00 PM
Ever been on a Maine hike or beach walk and come upon a big chunk of rock that seems out of place? Perhaps you asked yourself “How did this thing get here?” You might even be driven to take some pictures of it! Chances are good that you encountered a glacial erratic, a natural curiosity with a remarkable history.
Twenty thousand years ago Maine was completely covered by a southward flowing continental ice sheet (continental glacier) that spread outward from Canada’s Hudson Bay region. As this ice sheet moved across the landscape it picked up bits of bedrock and transported them to the south, eventually leaving them behind as glacial erratics when the ice melted about six thousand years ago. The classic glacial erratic has a rock type unlike the bedrock of the area in which it was deposited — an exotic “stranger.”
This talk will sketch out a bit of Maine’s history of glaciation, review how erratics are eroded, transported and deposited, and explore the role that erratics played as evidence in early thinking about the existence of prehistoric ice ages. (A bit of glacial erratic trivia might sneak in as well!)
ABOUT THE PRESENTER
D. Brooks McKinney, Ph.D.
Emeritus Professor of Geoscience
Hobart and William Smith Colleges
Geneva, NY
Brooks got interested in rocks and minerals in 1968 after discovering a book in his local public library called “Your Future in Geology” (hooray for public libraries!). One thing led to another: a Bachelor’s degree in geology from Beloit College; three years of work in Utah and Nevada as an exploration geologist; a doctorate from Johns Hopkins University; a geology teaching career at Hobart and William Smith Colleges; retirement and Emeritus status in June 2018.
Brooks and his wife Pat Blakeslee came to Maine on their honeymoon in 1981 and returned frequently over the next thirty plus years. Their attachment to Maine became permanent in 2018 with a move to Belfast, where they are now year-round residents. He still enjoys looking at rocks and fervently believes that librarians are among the finest people on the planet.
While you’re at the Rockport Library attending this talk, be sure to check out the exhibit of photographs of glacial erratics by Judy O’Dell (and related book art by Sandy Weisman) located in the Marine Room on the library’s main floor.
