Since the late Prof. Marsh's discovery of mammalian teeth and bones in the coarse grits of the Laramie Formation in Wyoming (U.S.A.), Mr. Charles Dawson, F.G.S., has persistently searched for similar fossils in deposits of the same nature in the Wealden formation of Sussex. These beds consist chiefly of coarse quartz-grains mingled with teeth of fishes and fragments of bones, and were originally noticed by Mantell under the name of ‘Tilgate Grit.’ According to Mr. Dawson's observations, however, they form only small lenticular deposits, and occur at several horizons in the Wealden Series.