No man shall take the nether or the upper millstone to
pledge. --Deut. xxiv.
6.
Note: The cellular siliceous rock called buhrstone is usually
employed for millstones; also, some kinds of lava, as
that Niedermendig, or other firm rock with rough
texture. The surface of a millstone has usually a
series of radial grooves in which the powdered material
collects.
{Millstone girt} (Geol.), a hard and coarse, gritty
sandstone, dividing the Carboniferous from the
Subcarboniferous strata. See {Farewell rock}, under
{Farewell}, a., and Chart of {Geology}.
{To see} {into, or through, {a millstone}, to see into or
through a difficult matter. (Colloq.)