GEOLOGY OF NORTHERN SHAN STATES AND YUNNAN 209 



dikes of a basic type are common and in some localities cover an 

 extensive area. 



Coggin Brown in his work in Yunnan did not attempt to map 

 the granite separately from the gneiss, but from the text it appears 

 very probable that the band of granite separating the gneiss from 

 the younger sediments south of the Shweli extends well north of 

 that river into Yunnan. 



The pecuUar type of topography and accompanying excessive 

 disintegration over a portion of the granite area has been mentioned 

 previously. 



CAMBRIAN (CHAUNG MAGYl) 



These rocks differ in no respect from the descriptions of them in 

 the neighboring sections, as given by previous writers. They 

 consist of slaty shales, phyllites, and quartzites, severely folded and 

 of rapidly varying strike. The band of rocks of the Kao-liang 

 series mapped by Coggin Brown in Yunnan just east of the Shweli 

 River in latitude 24° 40' is undoubtedly a direct continuation of the 

 Chaung Magyi of the Northern Shan States. 



LATE CAMBRIAN-ORDOVICIAN-SILURIAN BEDS 



These formations are all grouped together, as it is possible 

 to separate them only by careful paleontological work. The oldest 

 rocks of this group are of the most interest, as it is in the section 

 under discussion that they attain their greatest importance. They 

 have been, called the Pangyun beds by Coggin Brown. No fossils 

 have been found in them, but as they are conformably followed by 

 Ordovician beds they are themselves either late Cambrian or early 

 Ordovician. 



It has been generally assumed by other observers that a decided 

 break exists between the non-fossiliferous Chaung Magyi and the 

 fossiliferous Ordovician strata, but it seems possible that this may 

 have been due to the fact that favorable exposures of the intervening 

 rocks had never been observed. In this area numerous sections 

 were examined from the Chaung Magyi to the Silurian rocks, and 

 no decided break could be found, the Pangyun beds apparently 

 filling in the period between the Chaung Magyi and the fossiliferous 

 Ordovician. In this connection it is interesting to note that lime- 

 stone beds are present at various points in the Pangyun series. 



