Railroad, are very extensive deposits of coquina or shell limestone, filled with bitumen. As found, the material is very tough and difficult to break. When the bitumen is dissolved out with chloroform, there remains a mass of small shells, very light and porous, but with sufficient stability to form a rock. The shells contain from nine to thirteen per cent, of bitumen. While a large sum has been expended on a plant for extracting this bitumen, the enterprise has never proved a pecuniary success. In northern Texas, near the Red River, are extensive deposits of bituminous sand, which has been used locally for sidewalks with success. Across the Red River, near the Arbuckle Mountains, in the Chickasaw Nation, beds of bituminous sand occur of great extent. They extend across the country in anticlinal folds for miles in length. The material is not stone, as the sand falls into a powder as soon as the
bitumen is removed from it. When the material is broken into small pieces and placed in boiling water, the bitumen rises to the surface nearly free from sand, while the bulk of the sand sinks through the water clean. The bitumen thus obtained is of very superior quality for any purpose. Still farther north and east, near the town of Dougherty, several deposits occur. One is a mass of great extent of fragments of chert and limestone cemented together with bitumen. A mastic has been made by grinding this material. Another mass consists of a magnesian chalk, of carboniferous age, saturated with bitumen. Another is a mass of large shells filled with more than twenty per cent, of bitumen. Other deposits of loose sand occur in beds, saturated with ten per cent, of bitumen. These materials have been used separately and ground together for paving mixtures for street surfaces.
