42 



LA TOUCHE : GEOLOGY OF NORTHERN SHAN STATES. 



order to render it perceptible, but on entering a quarry in the 

 limestone it is almost everpowering, even at a distance of several 

 feet from the rock face. Even this evidence, however, is not con- 

 clusive in favour of the limestone having been organically formed, 

 that is, in the sense of being built up by living organisms, unless 

 it can be proved that the odour is really due to skatole. To my 

 mind the smell appears to possess a more sulphurous character 

 than one due to any organic compound, and to be derived from the 

 decomposition of the sulphide of iron (pyrrhotite) with which the 

 limestone is impregnated. 



Dr. Bleeck also draws attention to the presence of chondrodite, 

 forsterite, and garnet in the limestone of Nania- 



of Mogok by Professor Judd, and to the com- 

 parative rarity of corundum in the former, and suggests that the 

 difference is due to local variation in the character of the agents 

 that have effected the metamorphism of the rocks. In the Nania- 

 zeik area contact metamorphism, due to the intrusion of massive 

 dykes of granite, has predominated, whereas in the Kuby Mines 

 district pressure metamorphism has played the more important role, 

 with the result that in the latter area corundum is more abundant, 

 and the typical minerals due to contact metamorphism, such as 

 forsterite, chondrodite, and garnet, are either rarely found or are 

 absent. 



In the Annual Eeport of the Geological Survey of India for 

 1895, 1 Mr. Griesbach alludes to an examination 

 at S sSyin d COng! ° merate by Mr. Hayden of the ruby-bearing limestone 

 of the Sagyin Hills, in the Irrawaddy valley 

 north of Mandalay, and says :— 



" One of the most interesting facts established by Mr. Hayden is that the 

 limestone rests on the schists and gneiss, the junction being marked by the 

 presence of a conglomerate associated with a limestone breccia, thus proving 

 without doubt that this coarsely crystalline limestone is of sedimentary 

 origin." 



And again 2 : — 



" The crystalline limestone, in which such minerals as ruby, spinel, rubel- 

 lito and schorl occur, is found to be separated from the gneisses by a con- 

 glomerate composed of blocks of limestone, gneiss and quartzite." 



1 Records, Gcol. Surv. Ind., Vol. XXIX, Pt. 1, p. 9. 

 ■ Ibid. p. 60. 



