76 FLORIDA GEOLOGICAL SURVY-I5TH ANNUAL REPORT

collected clays in Florida that had crystals of selenite (one form of gypsum) as much as a half an inch in diameter.
 Rutile-TiO2. This mineral is probably widely distributed in clays, usually in small amounts. Few attempts have been made to identify it in clays. It rarely occurs in large quantities. Somers4 reports rutile as unidentifiable in three of the one hundred and twelve clays examined miroscopically by him, moderate in three, scarce in fifty-three, common in twenty, and abundant in thirty-three. Its effect is negligible except in white-burning clays. It usually occurs in microscopic grains.
 Ilmenitc-TiFe203. It is not definitely known that this mineral occurs in clays, but its occurrence is probable in those clays which have been derived from soda-rich and basic eruptive rocks. Ilmenite is a constituent of some of the sands along the east coast of Florida and its presence is to be expected in some of the clays of that region. Its effect is perhaps similar to that of rutile.
 Glauconitc-This mineral, often called greensand, is a hydrated silicate of ferric iron and potassium with aluminum and water in variable proportions, and usually mixed with other minerals. It is easily fusible and hence a high percentage of it is not desirable. It is olive to grayish-green in color. It occurs in many of the clays of the Atlantic coastal plain region and has been reported in clays in New Jersey1, Maryland2, and Georgia3.
 Chlorite-This term is applied to a group of secondary minerals which are hydrous aluminum silicates with ferrous iron and magnesium. Ferric iron may sometimes be present. It is found in small quantities in some clays. Its presence in the Cretaceous clays of Georgia4 and the Leda clays of Canada5 has been reported.
 Dolouile-CaMg (CO3)2. Dolomite is very similar in composition and properties to calcite. Alone it is highly refractory, but acts as a flux with other minerals. Dolomite is common in some of the clays of the Manatee River region.
 4Somers, R. E., Microscopic Study of Clays, in U. S. Geol. Survey Bull. 708, p. 292, 1922.
 1New Jersey Geol. Survey, Final Report, VI, p. 46, 1904.
 2Maryland Geol. Survey, Eocene, p. 52, 1901.
 3Veatch, Otto, Clay Deposits of Georgia, Georgia Geol. Survey, Bull. 18, p. 41, 1909.
 4Ladd, G. E., American Geologist, Vol. XXIII, p. 240, 1899.
 5Merrill, G. P., Rocks, Rock Weathering, and Soils, p. 335, 1913.