varieties of Chalcedony, include Garnet, Beryl, and Topaz.
Other
deposits in river gravel occur about 200 miles south-west of the
previous group at Wairagarh ; also 100 miles north-east to 200 miles
north-north-east of the Mahanadi deposits, near Jushpur, and about
Sumelpur. Many of these seem to have been of considerable importance at
the time Tavernier visited them (1560), but now they are not of great
interest as productive deposits.
A
large group of deposits extends south-west from Allahabad for 150 miles
or so, and is known as the Panna group. At none of these Panna mines is
the mineral actually found in the rock in which it was developed. In
some of the workings it occurs in thin beds of detrital rocks of great
age; in others, again, simply in sands and gravels derived from a
further disintegration of these detrital rocks. Only at Birjpur has the
material been cemented into a firm conglomerate. The associated
minerals do not seem to be of special interest, consisting only of
siliceous minerals in most cases.
In
the early part of the eighteenth century Diamonds were found in Brazil
in the gold washings in the State of Minas Geraes, though not
definitely recognised as such until they came into the hands of the
Dutch consul at Lisbon. They are usually said to have been found first
a short distance to the west of Tejuco, a town which afterwards became
known as Diamantina, lying some 340 miles north of Rio de Janeiro. The
mineral is found under different conditions in the various kinds of
workings, but the most important from the point of view of the origin
of the mineral are what are known as " plateau workings.2' These occur on the high p.s.
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