34. LA TOUCHE : GEOLOGY OF NORTHERN SHAN STATES. 



termination at Sagaing, opposite Mandalay. The change of strike 

 takes place near Wabyudaung (Wapudoung, C. B. B.) (A 1) about 13 

 miles to the east of the Irrawaddy, and is perhaps the cause, through 

 torsion of the strata, of the extraordinary broadening of the bands 

 of limestone in that neighbourhood, as shown in the map attached 

 to Mr. Barrington Brown's paper. On the eastern bank the 

 Palaeozoic rocks of the Shan plateau come right down to the 

 plains of the Irrawaddy, and the Archaean gneisses are found to 

 occur only in a few outlying hills rising abruptly from the alluvium, 

 including the Sagyin hills, mainly composed of the crystalline lime- 

 stone, which is largely quarried as statuary marble, 1 and Mandalay 

 Hill, which consists of the same limestone, traversed by veins of 

 granite. 



The gneisses appear again at the foot of the plateau scarp at 

 Kyaukse, where there are large marble quarries, 25 miles south of 

 Mandalay, and beyond this they form a continuous band, from 

 12 miles upwards in width, along the edge of the Southern Shan 

 plateau, extending to the sea near Moulmein. 2 



The following account of the gneisses and associated rocks and 

 minerals of the Ruby Mines area is taken from the abstract of the 

 paper by Mr. C. Barrington Brown and Professor 



Petrography. j ;y to aW (p 2?) ._ 



" The general mass of gneissic rocks composing the mountainous district 

 in which the ruby localities are situated are of intermediate chemical com- 

 position, and consist of biotite-gneisses, biotite-granulites, and, more rarely, 

 biotite-schists — rocks in which hornblende is rare or altogether absent, but 

 which, on the other hand, are often remarkably rich in garnets. Neither 

 corundum or spinel have been certainly detected in these rocks. 



" Interfoliated with these ordinary gneissic rocks, which form the great mass 

 of the mountains, we find rocks of much more acid composition, including 

 very coarse pegmatites and graphic granites, aplites and granulites (leptynite 

 or Weiss-stein), granular quartzites, and orthoclase-epidote rocks. The ortho- 

 clase of these rocks frequently contains inclusions of fibrolite and other minerals ; 

 it often exhibits the ' murchisonite ' modification and partings, and is 

 not unfrequently converted into ' moonstone '; still more complete alterations 

 of the orthoclase into epidote, muscovite, and kaolin being by no means 

 uncommon. In the rubellite district of Nyoungouk these acid rocks contain 

 pink and blue tourmaline (rubellite and indicolite), often beautifully zoned, 

 and it is probably from rocks of this class that the fine gem rubellites are 

 derived. 



1 Dr. T. Oldham, Appendix to Yule's Mission to Ava, 1858, p. 326. 

 C. L. Griesbach, Notes from the Geological Survey of India ; Records, Ge.ol. Sun; 

 Ind., Vol. XXIX, pp. 9, 60. 



* C, H. Middlomias, in General Rep. Qcol. Surv. Ind., 1899-1900, p. 128 



