256 LA TOUCHE : GEOLOGY OP NORTHERN SHAN STATES. 



CHAPTER X. 



PLATEAU LIMESTONE. 



Permo-Carboniferous or Anthracolithic Section. 



At various places on the Shan States plateau, especially towards 

 the south-east, patches of a limestone of a 

 andcharacL° CCUrrenCe character different from that constituting the 

 great bulk of the formation are met with, usually 

 as outlying masses, capping ridges and knolls with rugged precipitous 

 walls of rock. These limestones are generally dark blue, grey or black 

 in colour, with a much more strongly fetid odour than that of the lime- 

 stones below. Although the microscope shows that the matrix of the 

 rock is in all cases crystalline, the individual crystals are exceed- 

 ingly minute, and the rock does not exhibit the sandy texture 

 that is so characteristic of the ordinary Plateau Limestone, but is 

 much more compact and often possesses a conchoidal fracture. In 

 addition, these rocks are in many places highly fossiliferous, and in 

 most cases the microscope reveals in thin sections the presence of 

 minute fragments of shells, or of foramim fera of various kinds. 

 It has been found impossible to show these patches of rock on 

 the map attached to this Memoir, not only on 



Boundary uncertain. . .. , . . , 



account of its small scale, but also because 

 of the difficulty of finding any definite line of division 

 between them and the limestone beneath. On the plateau the 

 difference in appearance is easily recognisable, and the bound- 

 aries of each patch are fairly well defined, but I was fortunate 

 enough to discover a number of specimens of Fusulina elongata 

 at Tonbo (Loc. 27, B 5), at the extreme western edge of the hills, 

 in a band of limestone which appeared to pass laterally, as well 

 as vertically, into crystalline limestone indistinguishable from the 

 usual type ; and it is therefore by no means certain that there is 

 any noticeable difference in age between these compact, dark 

 co'oured rocks and the upper part of the ordinary Plateau Lime- 

 ConditionB of de- stone. It may be that the change of character 

 >"' M,, "" S - is not so much due to a difference in age 



as either to some local peculiarity in the conditions of accumula- 



