The glaciers ground softer rocks into smaller and smaller pieces.
The underside of the glacier picked up sharp pieces of stone and
rasped them across the earth. The glacier rasped polished grooves in
hard rock along Lake Superior’s northern shore and other places
such as Kelley’s Island in Lake Erie.Some Ice Age glaciers remain in northern Canada and Greenland. The Dynamic Great Lakes is available at Barnes & Noble, Amazon.com and many other online stores and fine bookstores.