A treatise of the earth called gypsum; with an account of the extraordinary effects of this earth as a manure, cheap and more productive to vegetation, than any hitherto ever made use of. [electronic resource] : Proved by a variety of experiments, as inserted in the several letters from correspondences of the agriculture societies of North America. Recommended to the farmers and gardeners of this country. Also an inquiry into the nature and philosophic cause, why this earth is so productive in vegetation, &c. By Charles Clarke, of Millbank-Row, Westminster