In England the favorite source of phosphates of lime is the "Cambridge coprolites." These are small, hard, gray nodules, obtained by washing a stratum, of about one foot in thickness, lying in the upper greensand formation in Cambridgeshire. Similar coprolites are found and mined in other districts of England, but they are of inferior quality, containing more oxide of iron and alumina. These give the tribasic phosphate of lime, which results from the application of sulphuric acid to the nodules, a tendency to "go back" to the insoluble condition. French nodules are of inferior quality from another cause. They contain very much silica, sometimes even forty per cent. The Cambridge coprolites are so much esteemed that buyers of artificial manure often stipulate that it shall be made from them. As a consequence the privilege of mining the ground is costly, sometimes as much as $1,500 an acre being paid. The yield is about three hundred tons to the acre. An English chemist reports that the South Carolina phosphate, made in factories situated in and near Charleston, ranks next in value to this Cambridge product. It contains 54 per cent. of tribasic phosphate of lime, 14 per cent. of carbonate of lime, 3-1/2 per cent. of iron oxide and alumina, 2-1/2 per cent. of fluoride of calcium, and 15 per cent. of silica. It consists of bone fragments derived from animal species which are now extinct. These bones have accumulated in old river beds, and the mining operations are compelled to follow the sinuosities of these streams. Though a supply derived from such sources is necessarily limited, the quantity known to be available is very great, and has been estimated to last a century with a yearly extraction of 50,000 tons. In addition to the river phosphate is a lighter deposit, occurring in a stratum of sand and clay about two feet thick; but this is not so valuable, though it is softer and easier ground. The river deposit is nearly black, and when ground makes a very dark powder. It is a great favorite, and in some respects the finest natural source of phosphatic manure in the world. RARE METALS FROM OLD COINS.