240 THE GEOLOGY OF THE MALAY PENINSULA. 
In Yunnan the succession of pre-Cambrian rocks is as 
shewn below. 
‘ = ‘ ee Uinicomtonmaniver 5 s 
2. Kao Liang system. Phyllites, quartzites, slates, 
and an occasional calcareous horizon. In part 
pre-Cambrian and part Cambrian. 
2 . 7 es Umconitornatiny ana: g 
1. A basal mass of gneisses and schists underlying 
all recognised groups. 
The basal gneisses and schists are so metamorphosed that it 
is impossible to determine their original character, except that a 
small provortion are recognised as metamorphosed sediments. 
They are intrude by granites which are relatively young, though 
some of them may be pre-Cambrian. 
In the Northern Shan States there is a large development of 
Archaean gneisses resembling those of South Western Yunnan in 
that they possess a similar N.H.—S.W. strike. The general mass 
are of intermediate chemical composition, and they consist of 
biotite gneisses, which are often remarkably rich in garnets, and 
which are interfoliated with more acid rocks, including pegmatites 
and graphic granites. The orthoclase of these last rocks is not 
infrequently converted into moonstone; often it is more com- 
pletely altered into epidote, muscovite, and kaolin. In Nyounggouk 
‘istrict these acid rocks contain pink and blue tourmaline (rubellite 
and indicolite), and it is probably from rocks of this class that the 
fine gem rubellites are derived. 
With the gneisses there occur certain subordinate rocks of 
basic and sometimes ultra-basic composition, mcluding pyroxene 
gneisses and pyroxene gramulites, and with these rocks, and parti- 
cularly with the ultra-basic types, certain remarkable crystalline 
limestones, containing rubies and spinels, are most intimately 
associated. 
A series of mica schists occurs to the south of the ruby mines 
area, and they seem to pass upwards into the Chaung Magyi series, 
so being either pre-Cambrian or Cambrian. 
The Kao Liang system in Yunnan is certainly m part pre- 
Cambrian, and partly Cambrian. It occurs as bands, running from 
north to south, which widen somewhat as they are traced to the 
south. In the Northern Shan States, south of Yunnan, the pre- 
Cambrian is represented by the Chaung Magyi system of phyllites 
and quartzites, and here it differs from that of Yunnan in contain- 
ing no calcareous bands. La Touche thinks, on lithological 
grounds, that the Chaung Magyi series may be Cambrian, for it 
diene only sh@ht signs we alteration, but a careful search of many 
outcrops revealed no traces of fossils, and as the rocks had been 
deposited, consolidated, thrown into folds and dislocated, and final- 
Jour. Straits Branch 
