whether it solidified underground as bosses and dykes or was ejected at the surface as volcanic matter it has not yet been possible to say. Much of this gneiss has been referred to the lowest horizons of the Archaean, the oldest geological system known, whilst other different types, together with the ruby-bearing crystalline limestones, show distinct resemblances to the Dharwar rocks of the Indian peninsula, which are metamorphosed sedimentary deposits of later Archæan age. A similar gneiss was observed in the Yamèthin district, and it is surmised that a more or less continuous belt of this rock extends from Yünnan to the vicinity of Moulmein. Intersecting in every direction the ancient Archæan gneisses are veins of granite which in a molten state has been forced into fissures.
The next oldest rocks have so far yielded no fossils, and must belong either to the Cambrian—i.e. the oldest known fossil-bearing system—or to an intermediate system between the Cambrian and the more ancient Archaean, or to both. They comprise what has been called the Tawngpeng system in the Shan States and the Mergui beds of Tenasserim. Whatever their precise age may be, their most characteristic feature is the complete absence of lime, the rocks consisting of schists, various altered forms of sandstone and clay, and an interesting series of lava flows and volcanic ashes ejected from neighbouring vents. The lavas in the Shan States strongly resemble similar lavas found in the Malani district of the Jodhpur State in Rajputana and are of much the same age. Amidst the volcanic ashes and lavas occur the important lead, silver, zinc and copper deposits of Bawdwin. In Tenasserim the Mergui beds, which probably form a more or less continuous belt with those of the Shan States, are also associated with rich mineral deposits, but in this case of wolfram and tin[1]. The Mergui beds are no greater in bulk than the granite which has been intruded into them. This granite has been
- ↑ See p. 74.
