This vast space of territory has not been examined scientifically, and but little is known of its condition except that it is diamond yielding. Since their discovery the mines have been worked with more or less activity with slave labor under the direction of companies of large capital. Skilled labor with the modern appliances of science has not yet been employed in these mining districts. And the condition of the country, its laws, and the controlling power of the diamond corporations, will render the application of scientific skill a difficult and hazardous task. The explorations are conducted in a primitive manner during the dry season, which lasts from April to October. They are made generally in the beds of the streams which have been dried up by the summer’s drouth. Rivers are sometimes diverted from their natural course, and their gravelly beds completely removed to sheds on the banks to await the rainy season, when water, which is required for washing, will be in abundance. The cascalho, a name given to the peculiar gravel, composed of quartz fragments mixed with sand and clay united with a ferruginous cement, which contains the diamonds, is then placed in shallow troughs, and a stream of water directed upon it until it is well cleansed, when it is removed and dried in the sun. The dried residue is then carefully searched for diamonds, and it is not always easy to distinguish them among a great variety of pebbles, of which the _débris_ is chiefly composed. Some of the diamond mines were of great extent and required many laborers to conduct the operations. That of Mandanga employed twelve hundred slaves in its excavations alone, besides many free persons engaged in other duties. The yield of the Brazilian mines at first was enormous, and one thousand one hundred and forty-six ounces of the precious gem were shipped to Lisbon in one year. The vast quantities of the gem thrown upon the markets brought the price of them down to five dollars per karat. Consternation speedily spread among the diamond dealers all over the world; and many of them, believing that the gems would soon be as common as transparent quartz, declined to invest largely, even at these low prices. But a panic was checked by the prompt action of the Brazilian Government, in claiming the working of the mines as a royal monopoly, and also regulating the supply. In this condition of affairs the working of the mines and the trade remain at the present day; but the African discoveries and free explorations may change this restriction and monopoly if the Cape fields continue to yield their present supply. According to the estimates of Baron d’Eschwège, the quantity of diamonds obtained from the Brazilian mines under the Government restrictions averaged between 1730 and 1814 thirty-six thousand karats annually, the cost of which amounted to nearly four dollars per karat.