THE GEOLOGY OF THE MALAY PENINSULA. 241 
ly subjected to denudation, before the accumulation upon them of 
strata containing Ordovician fossils, the stratigraphical evidence 
points to pre-Cambrian age. 
The Bawd'win volcanic rocks, a series of tuffs and ashes inter- 
stratified with layers of true rhyolites, occurs in some localities 
between the Chaung Magyi rocks and the lowest of the fossiliferous 
series (Ordovician). At Bawdwin the tuffs and ashes have been 
worked for silver for hundreds of years, and very large quantities 
of silver-bearing lead ores have been extracted. The mineralisation 
of the rocks occurred as a result of a great overthrust, im the 
neighbourhood of which they are intensely crushed and shattered. 
Ordovician. 
Fossiliferous beds of this age are known in three localities, in 
Western Yunnan, at Pu-piao, where they consist of sandy shales 
or mudstones with bands of impure, hard, nodular limestone, at 
Shih-tien, earthy Hmestones and slates, and at La-méng, calcare- 
ous slates and mudstones. The fossils show a marked resemblance 
to those of the Northern Shan States of Burma, as is to be ex- 
pected from the geographical proximity of the areas. In the North- 
ern Shan States the lowest beds of the Ordovician (lower Naung- 
kanevis), on the west side of the Plateau, consist largely of lime- 
stones, while to the east of the river Nam-T'u thev are represented 
by a soft sandy marl. The next highest beds (the upper Naung- 
kangvis) are represented, in the west, by intensely crushed shales 
in which all traces of the original bedding planes have been lost, 
and east of the Gokteik gorge, (river Nam-Tu), by bright purple 
clay stones. These strata, after the Plateau Limestone to be 
described later, are the most important formation occurring im the 
Shan States. : 
The Ordovician faunas of Eastern Yunnan and Tongking are 
of a different tvpe from these of Western Yunnan and the Shan 
States. 
Silurian. 
In Western Yunnan fossiliferous slates of Silurian age occur 
on Shih-tien Hill and a few miles further to the south, and tn 
East Yunnan Silurian shales pass conformably into the lower 
Devonian. In some parts of Tongking, the Silurian and Devonian 
are more or less non-fossiliferous owing to metamorphism. 
In the Northern Shan States there are thin bands of graptolitic 
shales containing the only fossils of undoubtedly Liandovery age 
that have yet been found in the East. They are overlain by sand- 
stones and conglomerates, followed conformably by sandy marls 
with layers of a very hard and compact limestone. The fauna is 
similar to that of a corresponding age in Northern and Western 
Europe, and absolutely distinct from the Himalayan fauna of the 
same period, as has been the case for all the underlying formations. 
With the close of the Silurian epoch, the barrier which separated. 
R. A. Soc., No. 86 1922. 
