ON THE RUBIES OF BURMA AND ASSOCIATED MINERALS. 
191 
chief areas in which they have been described are Ceylon, the Salem district of the 
Madras presidency, the district of South Rewah in the Bengal presidency (where, in 
the midst of the gneiss series, beds of corundum rock are found, with others of lime¬ 
stone, dolomite, magnetite, and quartzite), the North-Western Himalayas, Bokara, 
Burma, and the Shan States of Siam. 
In all these districts the rocks containing corundum appear to be highly crystalline 
gneisses, sometimes passing into schists, and frequently including masses of limestone 
and dolomite, the latter rocks being, as a rule, highly crystalline, and containing 
many silicates and other minerals (“ calciphyres and cipollinos ”). Intrusive masses of 
granite or pegmatite also occur. There is no evidence, so far as I am aware, opposed 
to the view that the whole of these rocks must be regarded as of Archaean age. 
Now, as has been so well shown by Lacroix, one very remarkable and striking 
feature of the gneisses of Ceylon and Salem, in which districts corundum also occurs, 
is the prevalence of bands of granulite and gneiss of more basic composition than the 
rest of the surrounding metamorphic masses. These basic gneisses and granulites 
contain anorthite* and various forms of pyroxene, and not unfrequently scapoJite, 
wollastonite, sillimanite (nbrolite), kyanite, andalusite, and calcite, as well as spinel, 
corundum, tourmaline, and other accessory minerals. As we shall have to show in the 
sequel, the gneiss series of Burma which yields the famous rubies contains a number 
of subordinate bands of these remarkable basic gneisses, composed of. pyroxene, 
anorthite, and scapolite, with many accessory and secondary minerals ; and in all 
their essential features these present the closest resemblances to the corundiferous 
rocks of Ceylon and the Salem district. 
It is only in comparatively recent years that the importance and wide distribution 
of the pyroxene-bearing gneisses and granulites has come to be fully recognised ; 
and there is still, unfortunately, much diversity in opinion and practice in respect to 
the names by which they are to be distinguished. The older writers designated them 
by the name of “ trap-granulite,” while Barrois, following the usage of Dana and 
Sterry Hunt, employs the term “ pvroxenite ” for them. This latter term, however, 
as Lacroix insists, is more properly applied to rocks, either “ massive ” or schistose, 
which are almost wholly made up of pyroxenes; and the last-mentioned author describes 
the rocks with plagioclase felspar and wernerite as “ pyroxene-gneisses ” (“ gneiss a 
pyroxene).” The Canadian geologists have called the same rocks after the predominating 
felspar, “ anortbite-gneiss,” and sometimes “ augite-syenite-gneiss,” or “ anorthosites.” 
The “ trap-granulites ” of Saxony, which were long ago carefully studied by 
Naumann,+ Sciieerer.| and Stelzner,§ have in recent years been made the subject 
* As long ago as 1802 Count de Boubnon pointed out the association of corundum with anorthite 
(“ indianite ”) and fibrolite in the Salem district; and in 1839 Gr. Rose gave the name of “ barsowite ” 
to the Ural variety of Anorthite which contains corundum, 
t ‘Jahrb. d. k.lc. geol. Reichsanst.’ (1856), vol. 7, pp. 766-771. 
-j. I’CLira Haul u. x. min., Ac.,’ 1873, p. 673. 
+ ‘ Neues Jahrb. f. Mil 
§ Ibid., 1871, p. 244. 
