r • PERMO-CARBONIFEROUS : PLATEAU LIMESTONE. 257 



tion of the sediment, resulting in a particular assemblage of organ- 

 isms ; or perhaps to a difference in the treatment to which the last 

 beds to be accumulated were subjected after their deposition, as 

 compared with the remainder. On the one hand, these patches 

 may have been of the nature of reefs, supporting an abundant 

 brachiopod and coral fauna, while the surrounding sea was occupied 

 mainly by mollusca, with their more easily decomposed shell struc- 

 ture ; that is to say, the conditions that gave rise to the Devonian 

 reef of Padaukpin may have been repeated at this period. On the 

 other hand, the fact that these highest beds, as shown by the 

 chemical analyses given in Table 7 (p. 188), are composed of 

 practically pure carbonate of lime, whereas the whole of the mass 

 underlying them has been converted into a dolomitic limestone 

 indicates a complete change in the history of this portion of the 

 formation ; perhaps, as I have already suggested (p. 193), a 

 replacement of the long-continued subsidence which must have ac- 

 companied the deposition of so enormous a thickness of rock by a 

 somewhat rapid upheaval. For these reasons I have made no 

 distinction between these rocks and the Plateau Limestone for 

 the present, but it will probably be found that when the Southern 

 Shan States are geologically surveyed, it will be possible to map 

 them as a separate formation. 



It may be remarked that no trace of these upper limestones 



Probable erosion be- ha& been foUnd alon § fche ed S e of the ton g Ue 



fore deposition of over- of Plateau Lmestone extending northwards 

 ***** beds - along the east bank of the Nam-Tu, where 



the latter appears to dip conformably below the red Jurassic 

 sandstones ; but as there was certainly some denudation of the 

 limestone before the Namyau series was deposited, the topmost 

 beds may have been swept away during the interval. At Kehsi 

 Mansam, in the extreme south east of our area, the Permo-Carboni- 

 ferous beds are seen almost in contact with the red sandstones, 

 but the section at that place, to be described below, is on tlie line of 

 a fault and greatly confused, and the exact relations between 

 the two sets of beds are not clearly seen. 



The first discovery of fossils in these rocks was made in L899 



by Mr. C. S. Middlemiss, in the Southern 

 States 11 " 0 " 00 m aD Shan States, where they are evidently more 



highly developed than in the Northern States. 

 In fact they do not occur at all on the line of the Wand al ay 



S 



