58 COGGIN BROWN : MINES & MINERAL RESOURCES OF YUNNAN. 



(b) It seems probable that Triassic strata were deposited 

 over a considerable portion of Eastern Yunnan and that they were 

 generally removed during the severe erosion which took place in 

 Pliocene times. The small areas which are found now owe their pre- 

 servation to faulting. They occur in the extreme south-east of 

 the province. The transgression of the Triassic sea covered a 

 surface exposed to long erosion during the Upper Permian, and 

 at fir^t formed lagoon-like expanses in which the lowest deposits 

 of the system were laid down as alternations of beds containing 

 terrestrial plant remains with others characterised by marine forms. 

 The three great divisions of the Trias are represented and well 

 marked off from each other by distinguishing faunas. As a rule 

 they are said to be very folded and even inverted. The uppermost 

 beds of the Lower Trias have a littoral facies and the passage from 

 the Werfen to the Mesotrias is a progressive one. The Meso- 

 triassic forms collected by Loczy at Tchung-tien in the far north- 

 west in Ssu-ch'uan are practically identical with those from the 

 extreme south-east of Yunnan, which tends to prove that similar 

 conditions prevailed over a very extended area. These conditons 

 entirely changed with the passage into the Upper Trias, the deepen- 

 ing of the sea attained its maximum, pelagic conditions set in, and 

 an invasion of cephalopods, marked by the especial development 

 of ammonites of the Tracliyceraiid.ee family, took place during the 

 Noric and the Carnic. A definite uplift commenced in the upper 

 Noric period and sandstones containing coal-seams were formed. 

 Similar conditions of a continental character probably existed 

 during the Rhaetic at any rate over Eastern Yunnan. 



My own view is that the transgression of the Triassic sea was a 

 slow and progressive one from east to west in Yunnan and that the 

 continental conditions indicated by the great deposits of the Red 

 Beds series persisted in Western Yunnan to a much later period 

 of time than they did in the east of the province. According to 

 La Touche the Trias is entirely absent from the northern Shan 

 Slates, which nevertheless contain Rha>tic and Jurassic deposits 

 of a marine character with rich faunas. Now Jurassic strata are 

 known to occur in Ssu-ch'uan, but no trace of them remains in 

 Yunnan, if they ever existed at all. These facts seem to justify 

 my assumption that the Red Beds series, though confined to the 

 Upper Permian in Eastern Yunnan may be of true Permo-Triassic 

 age further west, and that the marine conditions which set in in 



