The one on the bottom was called the bed stone and the upper one the runner.
On the south side of it the bed stone had been formed into a shallow trough.
The corn or other grain to be crushed is thrown into a groove which surrounds the hole in the bed stone.
A bed stone, slightly convex, is capped by a running stone somewhat concave.
Mill A represents a view, and mill B a section of the bed stone and curb.