ON THE RUBIES OF BURMA AND ASSOCIATED MINERALS. 
193 
(Kilimanjaro) by Mugge, # in Brazil by 0. Derby and Lacroix, + and in New Caledonia 
by Garnier and Heurteau.| 
In studying the series of gneissic rocks of Burma by the aid of the general descrip¬ 
tions and the specimens supplied to me by Mr. Barrington Brown, the circumstance 
which appears most striking is the marked difference in chemical composition between 
the various bed-like masses which compose it. From highly acid rock, made up of 
orthoclase and quartz, with a little muscovite, but no ferromagnesian silicate, we find 
every gradation—through normal biotite-gneisses and schists—into rocks made up 
of quartz, basic felspars, and pyroxenes (pyroxene-granulites, “ trap-granulites/’ and 
pyroxene-gneisses); and these, by the disappearance of the felspar and quartz, pass into 
pyroxenites and amphibolites. The tendency of the basic felspars to break up and 
give rise to minerals of the scapolite family, by a process which I have described in an 
earlier memoir,§ and which Lacroix proposes to call “ Werneritization,”|| side by side 
with the change of both enstatites and augites into arnphiboles, gives rise also to many 
interesting varieties of rocks. How far the associated limestones are to be regarded 
as resulting from still further alteration of the scapolite-rocks will be discussed in 
the sequel. 
For the purpose of convenient description, we may classify the various rocks of the 
Burma area according to the following table :— 
A. Rocks of intermediate composition forming the great bulk of the foliated masses of 
the district. 
1. Biotite gneisses. 
2. ,, granulites. 
3. ,, schists. 
These rocks often contain much garnet. 
B. Rocks of acid composition, intercalated with the common biotite gneisses, &c. 
1. Pegmatites and graphic granites. 
2. Aplites and granulites (“ Weissstein ”). 
3. Granular quartzites. 
4. Orthoclase-epidote rocks. 
C. Rocks of basic composition intercalated with the common biotite gneisses, &c, 
1. Augite (Sahlite, green diopside, &c.) gneiss. 
2. Augite-granulite (with garnet, &c.). 
3. Enstatite- (hypersthene) gneiss. 
4. Enstatite-granulite (with garnet, &c.). 
* ‘ Neues. Jahrb. f. Min.,’ etc., vol. 4, 1886, p. 577. 
t ‘ Bull. Soc. Min. Fr.,’ vol. 12, 1889, p. 266. 
+ ‘Ann. des Mines,’ 6th Seines, vol. 12, 1867, p. 1 ; ibid., 7th Series, vol. 9, 1876, p. 232. 
§ ‘ Mineralogical Magazine,’ vol. 8, 1889, p. 186. 
II ‘Bull. Soc. Min. Fr.,’ vol. 13, 1890, p. 35. 
MDCCCXCVI.—A. 2 C 
