Page:Popular Science Monthly Volume 69.djvu/284

280 and carbons escape them. This in part accounts for the reason why large diamonds and carbons are frequently found in gravel already washed and picked over. I have heard of places which have been washed for the fourth time and paid, though doubtless in some of these instances the later finds were due to disintegration of conglomerate which yielded up stones heretofore inaccessible.

The limit of a good man is to concentrate and pick over a cubic yard of cascalho per clay, but this presupposes that the cascalho is easy of access and that the water is near at hand. If the cascalho has to be taken from the cracks, crevices, caves, etc., and with the present methods of mining those are the only places with virgin material which are accessible, it is accumulated very slowly. When it is remembered that at the South Africa mines there is worked over 192,000 cubic feet per day, it can readily be seen why the output of Brazil with its few thousand of hand-workers sinks into insignificance, if indeed the diamonds are in Brazil to extract.

The mines of Minas Geraes have been worked regularly since their discovery, chiefly by hand methods until during the last ten years when some machinery has been installed to aid in the separation of the diamond-producing gravel from the clay and sand and later on in partly sorting the gravel prior to the final clean-up which is always by hand process. In Bahia a little machinery consisting of a few pumps, a gravel sorter and a so-called automatic separator, which does not separate, has been installed at Salobro, but it is being allowed to rust out, work at present being done by hand entirely ignoring the machinery. The only other machinery in the great Bahia district consists of a few pumps mounted by an English company on the São José river. This company has machinery in transit for mounting a small electro-hydraulic plant, but will still leave the clean-up to hand process instead of adopting the automatic table in use at South Africa.

The diamondiferous lands of Bahia are owned by the state and leased either as small claims or large parcels to parties or companies desiring to work them. About all of the known areas capable of work with groups without machinery have been preempted. The nature of the work already done has been such that many productive areas have been covered with tailings. The river beds and other productive sections which will necessitate machinery are still awaiting exploitation.