54 TOGGTN BROWN : MINE8 ft MINERAL RESOURCES OF YUNNAN. 



(h) Eastern Yunnan*— Deprat has recognised a Silurian hori- 

 zon to the north of Yunnan Fu, and another in the valley of the 

 Nam-ti, near the Tong-king frontier, where shales with Spirifer 

 tonkinensis appear to form a passage between the Gothlandian 

 and the Lower Devonian. 



(6) The Devonian System (Older Palaeozoic limestones). 



On the map the limestones of Devonian and Permo-Carboni- 

 ferous age are shown together because it is impossible to map them 

 separately without better maps, and also because in the ranges 

 between the Yang-tze and the Salwcen, they have been so infolded, 

 and in many cases altered, that it is doubtful if they will ever bo 

 distinguished separately in the complex where they occur. Their 

 distribution is best appreciated from the map itself. 



(a) Western Yunnan. — In this region the older Palaeozoic 



limestones are unfossiliferous and the most striking 

 thing about them is their universal brecciation, a cha- 

 racter common to the Plateau Limestone of the Nor- 

 thern Shan States. The prevailing rock type is grey- 

 ish-white or greyish-blue dolomite, crushed and broken 

 to an extraordinary degree and traversed in all direc- 

 tions by minute cracks and veins of secondary carbonates. 

 The Surface of the exposed rock is black, very rough 

 and irregular. It is hopeless to attempt to follow up 

 any definite horizons or to establish any divisions in 

 such a formation. 

 In the Northern Shan States identical rocks cover hundreds 

 of square miles of territory, yet in the whole of the 

 continuous expanse of limestone, extending from May- 

 myo to the Salween river, with one notable exception, 

 not a single determinable fossil has been recognised, 

 though thousands of outcrops have been minutely exa- 

 mined. The one exception is the remarkable Padaukpyin 

 coral reef which has yielded abundant fossils 

 characteristic of the lower part of the Middle Devonian 

 of Western Europe. 



(b) Eastern Yunnan. — The presence of strata of Devonian 



age in Eastern Yunnan has been known since Joubert's 

 account was published, but it remained for Deprat 

 to map and subdivide the rocks in detail and for Mansuy 



