appear to have been rich. Those containing tin are distinct and nearly virgin. The tin oxide occasionally occurs massive and pure, but for the greater part, exists in the form of minute grains, interspersed through a ferruginous and siliceous matrix from 3 to 6 and even 9 feet wide. This substance is soft and easily broken down with the pick at a trifling cost, but requires fine grinding for the satisfactory extraction of the tin. Several samples examined by the writer showed much uniformity of composition, giving 7 per cent of metallic tin. On grinding with water, some 50 per cent of the earthy matter is almost immediately carried off, when the residue, consisting of siliceous particles, requires further stamping to reduce it. On washing, the tin oxide remains as a fine white or light yellow sand.
Tin from the Berenguela district is said to be of a superior quality to any other mined in Bolivia. A fine, permanent water power, suitable for "Peltoa" wheel or turbine exists at a distance of 800 to 1,000 meters from the mines.
The tendency of tin ore to degenerate into pyrites is again illustrated in Berenguela, where, in one of the mines, this change occurs at a depth of 150 feet.
In addition to the deposits already mentioned, many others exist, though, hitherto, of less importance; while the ravines, descending from some of the mines such as Negro Pabellon, Morococala and Huanuni are more or less rich in stream tin and have been to some extent worked, the washed product giving 62 to 68 per cent.
The celebrated silver mines of Potosi have, for many years, furnished considerable quantities of tin, which has also been worked of late years in the mines of Porco. The conditions under which it occurs appear to be very similar to those met with in Oruro.
The total exportation of concentrated tin ore from Bolivia at the present time is probably not above 400 or 500 tons per month.
