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116
PRECIOUS STONES.
crystals without any sign of erosion, and it Has been noticed that where these associated minerals are more abundant the Diamond is more common also.
Gorceix (" Comptes Rendus," vol. xciii., 1881), has been led to conclude from an examination of this deposit that the Diamonds here occur in situ, that they have actually been formed in the Quartz " veins " which so frequently penetrate the rocks here. So far no Diamonds have actually been seen in the "veins," though they have been found adhering to Quartz and to the other minerals occurring in the " veins."
One cannot but wish more definite information was avail­able as to this deposit, especially as to the geological history of the trench and its contents and their relation to the surrounding rocks, the past physical history of the district, and most particularly the relation of the " veins " to the rocks they penetrate.
At Bagagem, some 200 miles west of Diamantina, in the Serra dos Pilons, are other deposits, famous as having yielded in 1853 the Star of the South, a fine stone of 254-1/4 carats. South of Bagagem, at Agua Suja, Diamonds have been found associated with Magnetite, Ilmenite, Butile, Garnet and Perofskite, in a ground-mass consisting of blocks of rock derived seemingly from rocks which are in situ close by.
At Grao Mogol, near the southern extremity of the Serra Diamantina, some hundred miles north-north-east of the town of Diamantina, there is a deposit of the gem in a sand­stone; this sandstone has green Mica developed along its bed­ding planes, and contains the same minerals as are associated with the Diamond in the itacolumite. This has led to the