310 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
seen, this being the granite, here much decomposed. The dyke at the 
adjacent wall rock is very much kaolinized. The dyke consists of 
orthoclase almost entirely converted into kaolin with very large and 
fine crystals of quartz, many of which are as clear and transparent as 
elass. Individuals up to 6 inches in diameter were seen, but it is 
stated that even larger ones were found. Crystals of lepidolite 
measuring 6 inches or more across the cleavage faces, as well as mus- 
covite and biotite and large, clear individuals of colorless topaz of 
perfect crystal form, were also found in the dyke. One of the latter 
had a diametral measurement of 31/4 inches. The dyke also contained 
small bunches of cassiterite here and there. The cassiterite, and the 
quartz crystals, sold to the Chinese traders for the manufacture of 
the various objects which the artists of that nation cut in quartz, were, 
it is understood, the chief products of economic value, and as these 
were not found in sufficient quantities to warrant the continuation of 
operations, work was abandoned and the openings are rapidly filling 
in under the action of the heavy tropical rains. 
Leaving this granite intrusion and continuing on to the east, after 
an interval where the rocks are covered, the limestone series is again 
seen in frequent outcrops and the picturesque village of Kathe is 
reached, lying in a valley surrounded by high hills. Many of the 
lower hills are crowned by pagodas and the presence of many of 
the “twinlone” referred to below, which are seen in various parts of 
the plain, show that the underlying gem-bearing gravels have been 
tested at a great number of different places. It is at Kathe that the 
chief operations of the Burma Ruby Mines (Ltd.) are now being 
carried on. The road then rises and continuing on over the same 
limestone-gneiss series for a further distance of 9 miles descends into 
the Mogok Valley in which les the little town of the same name. 
This is a most beautiful little valley, 10 miles long by 2 miles wide, 
and, like the Kathe Valley, is surrounded on all sides by hills, the 
highest reaching an elevation of 3,500 feet above the town, which has 
an elevation of 4,000 feet, clad with tropical vegetation, many pic- 
turesque pagodas being seen on prominent points and lending a dis- 
tinctly Burmese appearance to the scene. A small stream winds 
through lower ground. 
The beds of this series of limestones and gneisses, which are exposed 
almost continually along this section from Thabeikkyin to Mogok, 
strike north and south, although sometimes bearing a little to the 
east with a strike of as much as north 20° east. They dip uniformly 
to the east. The dip near the west end of the section is quite low,- 
but 10 miles from the Irrawaddy the dip increases to 30°. About 
milepost 12 the strata are much contorted, but to the east of this, 
after a covered interval, the well-defined north and south strike is 
