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DIAMOND MINES OF BRAZIL 199
and Andarahy cut through the mountains. Late reports indicate that there are rich deposits yet farther back in the mountains.
The
general character of the Brazilian diamond fields indicate a wide
upheaval of the basic granite rock leaving a very rough and broken
surface full of huge gullies and fissures. In these fissures, and in
basins or depressions in the granite, are deposits of disintegrated
material forming sandstones and conglomerates of varying hardness, in
which the diamonds occur. These deposits have in a large measure been
washed from the high places and again deposited in gullies and basins
that were the water-levels of the streams ages ago, and parts of these
have again been washed down to the banks and beds of the streams which
now exist. The diamonds throughout are in an altered material, and the
original character of the matrix is not surely known. The indications
are that during a period of disruption it was exuded from the interior,
since which it has been weathered and washed into a conglomerate of
water-worn fragments, and deposited in the process in all the fissures,
gullies, depressions and interstices of the surrounding rocks, that
lay in the path of the waters to catch it. Of the pink Lavras quartzite
beds of the Bahia diamond fields, J. C. Branner says in the Engineering and Mining Journal of
May 15, 1909, "Cases of diamonds in place in these quartzites have been
reported to the writer, but though he has never personally seen such
specimens, the geologic evidence is all in favor of the theory that the
diamonds and carbonadoes come directly from the Lavras beds." He gives
an analysis of the quartzite by L. R. Lenox as follows: Silica (Si02)
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