OUTLINES OF GEOLOGY OF YUNNAN. 49 



SUMMARY OF THE STRATIGRAPHICAL GEOLOGY OF YUNNAN. 



On the large map appended to this report I have shown the 

 areas occupied by various groups of members of the geological 

 column, in the regions traversed by myself ; accounts of these 

 journeys have already been published or are in preparation. The 

 reader who is desirous of studying the geology of Eastern Yunnan 

 is referred to the beautiful, detailed maps issued with Deprat and 

 Mansuy's memoir by the Geological Department of Tongking. A 

 map published with Loczy's work illustrates the geology of a small 

 strip of country in Western Yunnan, between A-tun-tzu and Ta-li 

 Fu. 



I shall now describe briefly the various rock groups : — 



(1) Crystalline Rocks. 



(1) The term is used hero to designate the gneisses, schists 

 and associated crystalline rocks which underlie all the recognised 

 groups and are separated from them by a profound unconformity. 

 These rocks are often intruded by granite and other rocks which 

 are of younger ages, but which it is convenient to consider with 

 them. The following groups of crystalline rocks are known in 

 Yunnan : 



(a) The frontier ranges of the Irraivaddy-Salween divide. — A 

 great band of crystalline rocks, upwards of 70 miles wide 

 from east to west in the latitude of Bhanio, forms the 

 hilly country between the Burma-China frontier and the 

 Irrawaddy-Sahveen dividing range in this region and 

 stretches for unknown distances to the north and south. It 

 may be connected with the Mogok gneiss of the northern 

 Shan States and Ruby Mines district. The typical rock 

 is a banded greyish-white gneiss of medium grain, com- 

 posed of quartz, felspar and biotite, with garnet as a 

 common accessory mineral. Fine-grained amphibole 

 schists, biotite schists and quartz schists are associated 

 with it. White and greyish crystalline limestones also 

 occur. It is intruded by dykes and large batholithic 

 masses of white and reddish-white granite. In the higher 

 parts of the rrrawaddv-Salween divide, the commonest 

 type of rock is a fine-grained, banded, black and white 

 mica schist occurring with muscovite, quartz and horn- 



