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
