As for the thin layer of sand over your shells, Jim, the glaciers had a hand in that. We have two pieces of property that are glacial end-morianes, the dumping grounds when glaciers retreated. Downstate we have a ridge of 10' of pure sand over clay substrate. Up north we have about 15' of pure sand. Oil/gas deposits are at about 4500' down up north, and as the source of those deposits was decaying organic matter, the terrain was obviously much different in a previous global era.
Have you seen the extrapolated maps of Michigan that show it as a rounded off, shorter peninsula? Those maps show the ridge in front of my house as the shoreline of a great sea. I presented the large sharks teeth we found on the beach to an anthropologist and that's were I got the information that there was a salt water sea north of Michigan which teemed with sea life.
