014 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
bedrock, a clay containing pebbles, and in this all the gems which the 
deposit contains are concentrated. This is known locally as “ byon,” 
and corresponds to the stoney clay which, in the gem region of 
Ceylon, occupies a similar position and is there known as “illam.” 
When working such a deposit the overlying barren clays are first 
removed and the underlying byon is then carefully collected and 
taken directly to the mill. 
Upon the removal of this byon, the surface of the underlying lime- 
stone is seen to present a curious appearance. It is a surface of solu- 
tion and an immense number of “ hoodoos ”—10, 20, or 50 feet high 
and of sharp jagged outline—rise from the general surface, if indeed 
there can be said to be one, while deep, irregular crevices run down 
into the limestone, often to great depths. When the residual clay has 
been entirely removed from the valley floor, as is the case in the ex- 
hausted workings in the valley running through the town of Mogok, 
it is almost impossible to cross the valley except on specially con- 
structed roads or paths owing to the extreme irregularity of the lime- 
stone surface, the spectacle presented when looking across the valiey 
being weird in the extreme. The byon lying in the pockets and 
depressions in the very irregular limestone floor and filling up the 
crevices penetrating it, is often very rich in gems and, although con- 
trary to law, the natives frequently, when unobserved, busy them- 
selves in digging out the byon from such holes and corners and wash- 
ing it for the gems that it may yield. 
The native methods of mining are three in number, namely, by 
loodwins, hmyaudwins, and twinlone. 
The loodwins are workings by which the byon in caves and fissures 
in the limestone is extracted and then washed. 
The hmyaudwins are cuttings driven into the rain-wash on the 
hill slopes, the extracted byon being washed by sluicing, water being 
brought from some adjacent stream. 
Twinlone—in this, which is the commonest method, pits are sunk 
into the alluvium of the valleys from 2 to 9 feet square, and by means 
of these the gem-bearing gravel is raised to the surface, often from a 
considerable depth. After a few feet have been excavated, strong 
posts, 12 feet in length, are driven in vertically around the sides of the 
pit and short timbers are fitted between adjacent posts, and a lagging 
of twigs and dry grass is provided to support the walls. As the sink- 
ing progresses, new posts are sunk. The excavated earth and any 
water which accumulates is raised to the surface by a bucket—or an 
old oil can—attached to one end of a bamboo balance pole swinging 
on a high bamboo frame as shown in Plate 1. As already mentioned, 
this device is also in use in Ceylon. A great number of these pits, 
each with its bamboo frame and swinging pole, are seen distributed 
far and wide over the plain of Kathe, showing the extended prospect- 
