Each stone measures 1.4 metres across and 0.35 metres thick, substantial enough to have ground considerable quantities of grain in their time, yet there is no building around them, no machinery, no obvious reason why they should be sitting here on a slope above a small stream feeding into Loch Fána.

The mill these stones once belonged to was a horizontal-wheeled type, sometimes called a Norse mill or clack mill, a design in which the water wheel lay flat beneath the millhouse and drove the upper grindstone directly via a vertical shaft, without the gearing required by the more familiar vertical wheel. Simple to build and suited to modest streams, this kind of mill was common across Ireland for centuries, particularly in the west. The structure at Middlequarter was apparently built in stone and was known locally simply as "the Mill". At some point it was demolished, and the materials were put to a very practical alternative use: road-building. The stones of the mill became the road surface somewhere nearby, leaving the millstones themselves stranded on the hillside, too heavy and too awkward to be worth carting away for rubble fill.