The Duke of Argyll (in connection with other evidences of a more conclusive kind, that, during some portion of the tertiary ages, there had been some subaerial volcanic action in the Hebrides) explained the mode in which pumice occurred in the Island of Tyree. The pumice was found to form a bed or layer along the line of an ancient sea-beach, and was in the shape of balls more or less closely packed together. These appearances seemed to indicate that they had come in on the waters of a tide or current in large numbers at a time. They were manifestly sea-borne; and the only question was as to the most probable source.