either as regards the extent of the deposits or the class of associated minerals; occasionally, as in the silver mines of Oruro and Potosi, it is more or less intimately mixed with iron pyrites and ores of silver; in other, and the majority of cases, it is more or less pure, forming the chief characteristic of the lodes.
In some instances, the deposits are to a great extent superficial; in others, they have been followed to depths of 1,000 feet, and still continue. The width of the veins or lodes is also variable, ranging from 1 or 2 inches up to 6 or 8 feet. In the tin mines proper, the ore is frequently very pure, containing 40 per cent, 50 per cent, and even 65 per cent of the metal, though in such cases the width rarely exceeds 2 feet; in other cases, almost pure tin oxide occurs in the form of crystalline grains and nodules in a matrix of tenaceous clay or in a ferruginous mass, forming the bulk of the lode, which then often presents a width of from 6 to 10 feet.
In the mines worked exclusively for tin, depths of 600 feet have not, as yet, been exceeded. The ore in some of these continues rich in the bottom, while in others it gives place to pyrites carrying more or less tin. The excessive freights to and from the Pacific coast have hitherto greatly retarded the development of the Bolivian tin mines, increasing the cost of ore exported, and rendering difficult the importation of suitable machinery, the down freights reaching £12 to £14 per ton, and the up freights £20 to £24.
Another evil hitherto has been the insignificant amount of capital in the country available for the industry, and the disinclination of foreigners to make any considerable investments in a region laboring under such disadvantageous conditions.
The miners have been, almost without exception, in the power of the merchants, who, to counterbalance the risks which they undoubtedly run, contract for the delivery of ore at low prices, charging at the same time a high rate of interest on all advances, the result being that only the richest mines or those most favorably situated have been able to avoid, sooner or later, a state of bankruptcy. The completion, however, to Oruro of the Antofagasta Railway is already producing a most beneficial effect. Deposits hitherto untouched and mines worked in a desultory manner with little or no profit will undoubtedly now be taken in hand, and may be expected to pay well, while those at present in production will largely increase their output with the aid of grinding and concentrating machinery. Water power is not usually available in the immediate vicinity of the mines and the primitive methods employed for grinding the ore by manual labor under rocking stones, or with small edge runners worked by mules, do not admit of any reasonable amount being treated. Hitherto, only the richer classes could be touched, anything below 10 or 15 per cent not paying expenses; in many of the
