OUTLINES OF GEOLOGY OF YUNNAN. 55 



to describe their fauna. They occupy a great expanse 

 of country between the Triassic geosynclinal in the 

 extreme south-east and the region of the lakes. Pure 

 limestones are said to be exceptional and the rocks 

 are of sandy, marly or shaley-calcareous types. The 

 Lower Devonian, and the Eifelian and Givetian of the 

 middle part of the system, as well as the Frasnian and 

 Fammenian divisions of its upper part are present. 

 They are all very fossiliferous and the forms from the 

 Eastern Yunnanese Eifelian. like the Paudaukpyin fauna of 

 the Northern Shan States, show close affinities with those 

 of the same age from the Rhenish provinces of Europe. 



(7) The Permo-Carboniferous System. 



(a) Western Yunnan. — The fossiliferous Permo-Carboniferous 

 limestones are always found in close association with the older, 

 metamorphosed limestones, which they usually seem to overlie 

 unconformably. They and their associated contemporaneous volcanic 

 rocks occupy a good deal of country in the valleys of the 

 Salween and Mekong and in the Yang-tze valley north of Ta-li Fa. 

 The older limestones tend to give rise to rugged hill-tops covered 

 with screes, or to vertical- sided canons, while the Permo-Carboni- 

 ferous build wider valleys and form gentler slopes, through 

 the soil of which their smooth isolated outcrops protrude. The 

 commoner types are dark grey, or greyish-blue, massive limestones 

 with a compact texture, exhibiting bits of shelly fragments and 

 foraminifera in thin sections, whereas the older limestones merely 

 exhibit recrystallized calcite and dolomite. From these rocks 

 I have made large collections of fossils which unfortunately have 

 not as yet been examined by a specialist. Until they have been 

 described it is safer to make no remarks about the probable age 

 of the rocks and their affinities. 



Volcanic activity was very prevalent in Yunnan whilst these 

 limestones were being deposited and beds of tuff and ash, inter- 

 calated with andesitic, doleritic and basaltic flows, are commonly 

 found amongst them. In some localities they form the greater 

 part of the series. 



(b) Eastern Yunnan. — The detailed study of the Permo-Car- 

 boniferous rocks of Eastern Yunnan has been carried much 

 further than in the case of those of the more westerly parts of the 



