In addition to these native products, the mineral riches of the province are various and valuable. The silver mines of Uspallata have at times been very productive, and in other parts of the same range veins, both of silver and copper, are known to exist, though want of capital and labourers has hitherto prevented their being opened. With respect to the working of these mines by English companies, and in the English manner, the best opinions seem to agree that it would not answer to make the attempt. Mr. Miers carefully examined the mines at Uspallata, and has given a particular account of the mode in which they are worked by the natives, and of the process resorted to for separating the silver from the ore. At the time he visited them they were not yielding more than two marks per caxon:[74] a very low average, upon which he has taken the trouble to make calculations to show that the English mode of smelting can never be brought into competition with the process of amalgamation as practised in South America. He says,--"To ensure economical results the aid alone of the people of the country, as well as the application of their peculiar habits and management, must be resorted to: wherever English improvements are attempted to supersede the old methods, such trials would be attended with loss. "No one," he adds, "can doubt but that in the barbarous mode of operation followed in Chile great loss of product is occasioned; but when this loss is placed in competition with the increased cost of labour, materials, and management necessary to ensure a greater amount of produce, the inference is irresistible that it is better to put up with this loss than to expend a sum of money far beyond the value of what can be obtained by adopting the improved methods used in countries where facilities abound which can hardly be procured at any price in Chile and La Plata." Captain Head, after seeing them, came to a similar conclusion: he considered that, although they might yield a liberal return under the more economical plan of employing native labourers properly directed, and at the ordinary low rate of wages paid for such labour in that part of the country; from the want of water, wood for fuel, and pasturage for cattle throughout the region in which they are situated, they would not repay the cost of working them by machinery, or by an English establishment. In all this part of the Cordillera is to be found an abundance of limestone, gypsum, alum, mineral pitch, bituminous shales with appearances of coal in many places, slates, and a variety of saline deposits, amongst others common and Glauber salts.