GEM DISTRICTS OF CEYLON AND BURMA—ADAMS 315 
ing operations which have been carried out in this area, which is at 
present the largest producer in the Mogok concession. 
The Burma Ruby Mines (Ltd.), however, desiring to work these 
deposits on a large scale, adopted western methods of excavating and 
transporting the materials to be handled, and built mills provided 
with modern concentrating machinery for the purpose of separating 
the gems. 
The workings at the town of Mogok, as they appeared some years 
ago when mining here was at its maximum development, are shown 
in Plate 7, which is taken from a photograph reproduced in Escard’s 
“Les Pierres Precieuses” (Paris, 1914). This stretch of alluvium 
has now been worked out. The company is now working at Enjouk, 
on the margin of the Mogok Valley, as well as on a small scale at 
Bigom, Nanyasen, and other points, but its chief operations are now 
centered at Kathe, 8 miles to the west of Mogok. Unfortunately the 
rubies here are very often coarse and rough and not of the best color. 
At Kathe the geological conditions are the same as those at Enjouk 
and as in the old exhausted workings at the town of Mogok. The 
country rock is white crystalline limestone, often holding numerous 
flakes of graphite, phlogopite, and other minerals, with many inter- 
stratified bands of harder silicate rocks, chiefly plagioclase-scapolite 
gneiss resembling the limestones in color and a few other allied 
gneisses. One darker band was found to be composed essentially of 
a plagioclase and a brown hornblende, with a little pyroxene, biotite, 
scapolite, and iron ore as accessory constituents. Nothing that could 
be recognized as an igneous intrusion was seen in the workings. 
These rocks under conditions of secular decay and solution present 
the remarkably irregular “hoodooed” surface already described, 
covered with a mantle of residual clay. This, with the underlying 
limestone series, is seen in Plate 5, which is one of the working faces 
at Kathe. The byon lies directly on the irregular limestone surface 
and is overlain by the barren clays, 
The byon is brought to the mill in trucks, hauled from the work- 
ing face by an endless wire cable, and thrown first on a grate of 
_ spaced iron bars, which separates the large pieces of rock. The 
material which falls between them goes to two successive sets of 
revolving trommels into which water is fed. The coarser material 
from these goes directly to a table and is hand sorted by one of the 
company’s officers. Here, when the writer was visiting the mill, a 
ruby rather over 1 inch in diameter was found. 
The finer material from the last set of trommels goes into diamond 
washing pans, the gravel which is retained by these representing 
1 per cent of the original byon fed to the mill. This is then carried 
to a series of jigs which reject three-quarters and keep one-quarter 
of the product received from the diamond washing pans. This 
