millstone

As it is the circular Motion of the Mill-ſtone which brings the Corn out of the Hopper by Jerks, and with a Velocity depending upon that of the Stone, other Grains are always ſucceeding, which raiſe it anew, and the Flower just made being no longer preſs'd is carry'd away into the Boulting Mill by the Circulation of Air that the Mill-ſtone puts into motion, which makes a whirling there.

In North America the millstone grit, and a grey sandy and slaty rock beneath it, occur three times; and it is exceedingly difficult to distinguish these rocks in hand specimens, without the aid of organized remains. And remains are almost exclusively confined to the grey rocks. Common quarrymen, farmers, and foreign geologists, apply the names, greywracke and millstone, to all these rocks promiscuously; neither having observed their different relative positions.

Paying the mortgage every month is a millstone round their necks.