The
gems found are corundum, spinel, zircon, iolite, topaz, tourmaline,
beryl, and chrysoberyl, the latter in the varieties alexandrite and
cat's-eye. The report goes into full details of the localities, the
variations in the character, and the situation of the ilium, the methods of working, etc., and is accompanied by two maps.
Precious stones in India.—Although
India has long been associated traditionally with gems and gem
production, it yields at present but a small part of the world's supply
of such minerals. It is curious to find the statement made by the
director of the Indian Geological Survey, Dr. T. II. Holland, in a
recent report," that all the gems produced in that country " do not
approach in value the unset stones and pearls imported," which, during
the period covered by his review (1898-1903), had an average value of
over half a million of pounds sterling per year.
In
this review a special section is given to gems, of which by far the
most important are the rubies of Burma. The diamond occurrences are
described almost exactly as given by Mr. Sarratt C. Rudra, and cited in
the report of this Bureau for 1903.b
For
the rest, a few notes are added here: The blue sapphires formerly
obtained in the Kashmir State appear to have been exhausted of late,
and no records are procurable.
Ruby
spinel is a common associate of the true ruby in Burma both in the
gravels and in the limestone rock, and is often mistaken for it.
Another
Burma gem stone is the red tourmaline (rubellite). and some attempts
have been made to work it, as it is of fine quality. The data of
production, however, are very variable and imperfect. The value of the
output was estimated at £1,240 in 1900, but was barely £200 in 1903.
There
is considerable garnet production in Jaipur, in the mica schists of
Rajmahal; also near Sarwar in the adjacent State of Kishengarh. Data
from the former are not procurable, but the output from the latter
varies widely, its value ranging from £2,000 to £10,000 per year.
Methods of rock and fossil section cutting.—A
remarkable piece of work has lately been accomplished in the cutting of
large and very thin sections of silici-fied cycads, by Mr. R. G.
Wieland, of Yale University. This work, and the studies which it was
designed to illustrate, are presented in a bulletin illustrated by 12
heliotype plates about to be issued by the Carnegie Institution." The
material consisted of the cycadaceous trunks of Jurassic and Cretaceous
age, which have been found in some abundance within recent years in
Maryland, Dakota, and Wyoming. Among the latter, especially, the
details of structure are preserved in great perfection in the
silicified mass, and it has been possible by this most careful and
skillful piece of work to illustrate accurately the peculiar features
of these fossils. The sections measure from 10 to 12 centimeters in
length and from G to 10 centimeters in width. They are cut to the
fineness of one-tenth to one-fifth of a millimeter, and polished on
both sides and mounted on glass plates on balsam. Mr. Wieland believes
that with time for the devising of further appliances, it will be
possible to cut thin sections even from entire trunks.
