1895.] The Rubies of Burma and Associated Minerals. 391 



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. 



Of still greater interest are certain other subordinate rocks of basic 

 and sometimes ultra-basic composition. These include the remark- 

 able pyroxene-gneisses and pyroxene-granulites, which have in recent 

 years been described as occurring in so many widely- scattered regions 

 such as Ceylon, Southern India, Central and Southern Europe, 

 Norway and Sweden, Brittany, Spain, Algeria, Eastern, Western, 

 and Southern Africa, the United States and Canada, Brazil, and New 

 Caledonia. In these rocks the felspars are for the most part basic 

 ones, near to anorthite ; the crystals almost always exhibit the phe- 

 nomenon described by French petrographers as "quartz of corro- 

 sion," and the partial or complete transformation of these felspars 

 into scapolite (" werneritisation ") can frequently be traced. The 

 ferro-magnesian silicates are represented by many varieties of augite 

 (sahlite, diopside, and aegerine), of enstatite (bronzite and hypers- 

 thene), and more rarely of hornblende. Garnets are a frequent and 

 abundant constituent in many of these rocks, which, in their acces- 

 sory minerals and their structures often exhibit many features of 

 striking interest. By the gradual disappearance of the felspars from 

 these rocks, they pass into remarkable varieties of pyroxenites and 

 amphibolites. The chief varieties of these rocks, which are now 

 described from Burma, are the following : Augite-gneiss (with 

 sahlite, green diopside, &c.), augite-granulites (very rich in garnet), 

 enstatite-gneiss (with bronzite or hypersthene), enstatite -granulites 

 (rich in garnet), scapolite-gneisses, scapolite-granulites, pyroxenites 

 and amphibolites of many varieties, and lapis-lazuli (lazurite-diopside- 

 epidote rock). Many of these rocks contain crystals of calcite scat- 

 tered through them. 



It is with these basic rocks, and more especially with the ultra- 

 basic types last mentioned, that the remarkable crystalline limestones 

 that contain the rubies and spinels are most intimately associated ; 

 indeed the passage of rocks consisting of various silicates with a 

 few calcite crystals into masses principally composed of calcite, but 

 with the silicate minerals and oxides dispersed through them, is of 

 the most insensible kind. Some of the ruby-bearing limestones are 

 highly micaceous ("cipollin os "), others are " calciphyres," in some 

 of which the individual calcite crystals attain enormous dimensions. 

 With the rubies and spinels are found a great number of oxides and 

 silicates, both original and secondary, with much graphite and pyr- 

 rhotite. 



In the gravels and clays of the district fine specimens of the mine- 

 rals derived from the atmospheric degradation of the limestones and 



