See quotations.
1786. In one of the Desks they found Thirteen milled Dollars,… and a Cobb Dollar; the latter being a Counterfeit was thrown on the Floor.—Maryland Journal, March 14.
1789. The public are hereby cautioned against taking a certain kind of cob-gold, which is now in circulation, but which has been refused by the banks of New-York and Boston in consequence of its having been proved by the hydrostatic balance to be one third alloy…. These pieces, each of which weighs 17 penny-weights, may easily be distinguished from the true ones by their roughness, which is caused by the sand in which they are cast.—Id., Jan. 2.
1793. At times to this day … there are King William and Queen Mary’s coppers picked up, and pieces of silver called cob-money.—Levi Whitman, ‘A Topographical Description of Wellfleet,‘ quoted by Thoreau, ‘Cape Cod,’ p. 148 (1865). (N.E.D.)
