THE GEOLOGY OF THE MALAY PENINSULA. 239 
world’s richest tin deposits. A coulisse between these two begins 
in Siam, and runs in a direction shghtly west of south into Upper 
Perak whence it extends as a granite mountain range passing near 
Taiping to the Dindings, and, ‘according to a Dutch ceologist, along 
the east coast of Sumatra, masked by more recent beds, passing 
through Billiton in an easterly direction, and turning northeast 
through the centre of Borneo, and up through the Philippines out 
of our area. Another important fold or coulisse is represented by 
the Annam cordillera, perhaps continued south into either the 
Anamba Islands or the Natuna Islands, and thence into Borneo. 
The Mesozoic folding was more intense, in the greater part 
of the area, than that which affected the Tertiary rocks, and this 
is shown by the fact that the Tertiary rocks often have gentle 
undulating folds, whereas the Palaeozoic rocks, upon witch they 
uneonformably rest, are vertical or highly inclined. However, the 
Tertiary beds were subjected to intense earth-movements in some 
districts, as, for example, in Eastern Yunnan, and after folds had 
been denuded away, great faults cut across the region, at about the 
end of the Phocene, probably giving rise to the lakes in which the 
late Tertiary fresh- water beds were laid down. 
In Western Yunnan there were strong folding movements 
after the Permo-Carboniferous and before the upper Permian 
period. 
Stratigraphical Sequence. 
The mountain folds which were described above have been 
eroded, with the result that there are now exposed strata of al] 
ages, since the period before the dawn of hfe on the earth. Atl 
the countries of our area, south of Burma, formed part of the 
Palaeozoic continent of Gondwanaland, which remained as a per- 
manent Jand surface from pre-Cambrian times until Devonian or 
Carboniferous, and no fossiliferous rocks of pre-Carboniferous age 
are known, except in the north. Earth-movements and aerial denu- 
dation of the later rocks, in Yunnan and the Shan States of 
Burma, have brought these old rocks to the surface. 
Pre-Cambrian. 
Many Dutch geologists have expressed the opinion that the 
“oudeschiefer” (old schist or old slate) formation of the Hast 
Indies is, in part, pre-Cambrian, though they admit that where it is 
not overlain by Carboniferous limestone it may be of Mesozoic age. 
Some of these geologists have correlated the “‘oudeschiefer” with the 
schist series of the Malay Peninsula, the greater part, and perhaps 
the whole, cf which is of Rhaetic age and later, so it appears that 
there are good grounds for not lyet accepting any part of the 
“oudeschiefer” as pre-Cambrian. In this account we will postpone 
a description of this “old schist” formation until we are describing 
the younger Palaeozoic and the Mesozoic formations. 
R. A. Soc., No. 86 1922 
