80 rucr.lN BROWN : MINES & MINERAL RESOURCES OF YUNNAN. 



wood to start the combustion. Small passages are left as channel 

 for the gases and air. Smaller coal is then gradually piled on top 

 and the outer hemisphere covered with earth, which is broken 

 through when the operation is complete. Small air holes are lext 

 at the junction of the inner and upper chambers. In this way 

 a hard coke of excellent appearance is produced, though it tends 

 to be somewhat tumid when very bituminous coal is used. 



Owing to the practice of mining outcrop material and oi allowing 

 shaly partings to be mixed with the coal as this does not interfere 

 with the preparation of the sun-dried briquettes already referred 

 to it is almost impossible to obtain fair samples from stock heaps 

 at' the mines. In mining no selective care of any kind is exercised 

 and inclusions of shale and dirt bands, or pieces of the floor and 

 roof of a working are matters of no consequence at all. 



General Remarks on Yunnan Coals. 



Deprat has summarized the views of his colleagues on the 

 Triassic coals of Yunnan as follows (De., p. 245) :— 



" The Triassic coals have very variable qualities : those of the 

 Werfen are the best coals in Yunnan and yield an excellent, 

 solid, dense coke. The seams are of great extent ; these coals 

 are not so friable as those of the Moscovian or of the Upper Trias. 

 The Middle Trias coal is always deceptive and was formed under 

 conditions which produced irregular beds distributed in the sand- 

 stones. Those of the Noric on the contrary appear better ; the 

 Ni-ou-ke coal is typical ; they produce a friable coke, but they axe 

 rich in volatile matter and are gassy." 



The analyses of the Mesozoic coals of the Yunnan Hsien basin 

 show that this material is lower in volatile matter than the Triassic 

 coals of Eastern Yunnan and with one exception they can only 

 be classed as poor material. Yet I am inclined to regard this 

 poverty in volatile matter as a result of superficial atmospheric 

 action on outcrop material rather than a quality inherent in the 

 coal itself. Further north, in the Yangtze valley, the coal of the 

 Ma-ch'ang and Chiu-ya-p'ing Hsien districts, which is probably 

 of the same age as that of the Yunnan Hsien basin, possesses, as 

 Leclere's analyses show, a higher percentage of volatile matter 

 and a better calorific power, than any of the other Triassic coals 

 of Yunnan. It also gives an excellent coke. The seams of this 

 region are mined deeper than those further south. The high ash 



