46 



LA TOUCHE : GEOLOGY OF NORTHERN SHAN STATES. 



is obtainable from many of the streams that drain them. In this 

 respect the rocks of the Bawdwin series are the most important, 

 for they contain the only really promising deposits of metallic 

 ores that have yet been discovered in the Shan States. 



Mica Schists of Mbng Long. 



To the south of the gneissic area in the Ruby Mines District 

 . , a broad bolt of mica schists is found 



Area occupied. . 



occupying the wide valley of the Nam-pai, 

 in which the town of Mong Long, the capital of the sub-State of 

 that name, is situated, and the spurs of the range of hills to the 

 south of it. The strike of these beds shows more irregularity in 

 direction than that of the gneiss, probably due to the intrusion 

 of thick dykes and bosses of granite along the boundary, but in 

 general it is nearly east and west. The western termination of 

 the band is somewhat uncertain, owing to the almost inaccessible 

 nature of the middle portion of the Nam-pai valley, where it 

 meets the south-westerly extension of the Mogok gneiss ; but as 

 the lower portion of this valley, from Setsigon (B 2) to Ze-haung, 

 coincides with a N.-S. fault, it is probable that the mica schists 

 are cut off by an extension of this fault to the north. The south- 

 ern boundary of the mica schists is very indefinite, and the line 

 drawn on the map must be considered as only roughly approxi- 

 mate. On the hill slopes it is exceedingly difficult to find any 

 outcrop of the schists, for they are easily weathered, and all that 

 can be seen in the few exposures visible along the paths are patches 

 of micaceous clay in which the original foliation planes are marked 

 by splashes and lines of bright scarlet, resulting from the oxida- 

 tion of the iron in the rock. And since the rocks of the next 

 succeeding formation weather in much the same way, though not, 

 as a rule, with the same brilliant colours, it is not at all easy to 

 decide where to draw the line between them. Indeed it is not 

 unlikely that there is a gradual passage from one to the other 

 formation, and that the higher degree of alteration of the mica schist 

 is due to contact metamorphism, induced by the intrusive granite 

 alluded to above. For it has been noticed elsewhere that when 

 dykes and bosses of granite are intruded among the slates of the 

 Chaung-Magyi series, they have a tendency to become schistose. 

 The rock is an ordinary biotite schist, composed mainly of granular 

 quartz and biotite, the latter in large quantity 

 in lath-shaped crystals, arranged parallel to the 



