This image shows the unexpected fate of a large quantity of grind stones which had been manufactured nearby but found no owners. They are used for shoreline stabilization for which they are also eminently suitable, given their great size and hardness.
The description states:
2085 MICHIGAN THUMB SCENERY
Abandoned grindstones, once a thriving industry at Grindstone City, Michigan.
—Grindstone City is an unincorporated community at the eastern end of Port Austin Township, located at the northern tip of the ‘thumb’ of the Michigan peninsula. The shore shown here is part of Lake Huron.
This postcard is dated 1955.