The author, after some general remarks on the Infusoria generally, and especially on , their occurrence in the fossil state, mentioned that the earth in question had been discovered by the Duke of Argyll at Knock, near Aros in Mull, and its geological position briefly described by him to the Society, two years ago. The author had undertaken an examination of it, and had found it to contain, besides Phytolitharia, silicified pollen of grasses and coniferse, and spicules and gemmules of fresh-water sponges, the unprecedented number of about 60 species of Diatomaceæ. He had consulted the Rev. W. Smith, who had observed in it the following 59 species, all belonging to fresh water, which he named, the names being those of his forthcoming Synopsis, and one species which he cannot at present refer to any known form.