In the Silurian system in New York, Ontario, Michigan, etc., several beds of rock salt and gypsum occur, indicating that there were formerly a number of separate evaporating basins in that region. The beds of salt vary in thickness from a few inches to over 300 feet, as at Tulley, New York. At Goodrich, Ontario, 6 beds of salt from 6 to 35 feet thick have been penetrated in a single well. With the salt in this the Salina formation there are many beds of gypsum. In rocks of Carboniferous age in Michigan, other extensive beds of salt and gypsum have been discovered. In Louisiana, Texas, Utah, and other States, salt and gypsum occur in Mesozoic and Cenozoic rocks. One of the most remarkable of these deposits is beneath small islands in the Gulf of Mexico off the Louisiana coast. On Jefferson Island, for example, rock salt was reached recently at a depth of 260 feet beneath Cenozoic rock, and was penetrated for over 1,800 feet without reaching the base of the deposit. The supply of salt stored in the rocks, and the natural brines of the arid region, such as the waters of Great Salt Lake, afford an inexhaustible supply upon which comparatively small demands have thus far been made. In addition to salt and gypsum there are other substances that have been accumulated in a similar manner, such, for example, as sodium sulphate, of which large beds occur in the desiccated lake basins of the arid region, sodium bromide, which is obtained from some of the ancient brines pumped from deep wells in Michigan.