It's one of those long winter nights when Minnesotans ought to catch up on projects. One of mine, long neglected, is blogging about MN geological history. I couldn't remember where I left off so I looked it up. I found the last topic I covered was the Cenozoic which brings us up to the Quaternary, 2 million years ago to the present.
It's interesting. The first few paragraphs describe erratics but do not mention them by name. It talks about a 20 ton fine grained green-gray rock different than the pink granite bedrock upon which it rests on the floodplain of the Chippewa River. Near the quartzite bedrock of Rock County are large granite fragments the Indians called the Three Maidens. In Dakota County a granite boulder was honored by a continuous wash of red ochre, probably because it was obviously different than the bedrock. This was long before European settlement. These rocks were all carried by glaciers. They are called erratics, which was the subject of my acrylic painting (of Finnish erratics) of which I am so proud to say was purchased by an employee of the Guggenheim and is displayed in her private gallery.