I. Introduction. Samples of sand were carefully collected from all the principal exposures on the outcrop of the Pebble-Beds in Nottinghamshire. It was cleaned in hydrochloric acid, sifted, and then separated by means of Thoulet's Solution having a specific gravity of 2⋅77. Enough of each sample (namely, 2 ounces) was taken to give a heavy residue sufficient to weigh and to mount as permanent objects for the microscope. II. Physical Characteristics of the Sand. The sand in the exposures is more or less coherent, in many cases taking on the appearance of hard rock. It may, however, when dislodged (the cement being mainly ferric oxide) be easily crumbled, often between the fingers. At depths of 102, 211, and 307 feet, cores at the Farnsfield borehole, near the Midland Railway Station, showed the rock to be compact, hard, and very calcareous Microscopic examination proved this to be the only real difference when compared with samples taken from the exposures. The sand varies in texture and colour, coarse-grained material largely predominating; but the following distinct types may be recognized:— 1. A coarse sand, whitish yellow to buff and brown in colour, found in most exposures. 2. A reddish sand of medium coarseness, found in all the principal exposures. 3. A dark brownish-red sand of fine texture, used for moulding purposes, found especially at Whisker Hill Quarry near Retford, and at Bestwood Warren. 1 Samples 2 were all taken from No. ‘2.’ Ordinary bedding may be observed, but false bedding is