CORUNDUM (RUBY): OCCURRENCE IN BURMA 271 



ranges in this district, and which, according to the investigations of Dr. F. NoetUng, of the 

 Indian Geological Survey, is of Upper Carboniferous age. These rocks were originally, 

 compact limestones of the ordinary kind, which have been altered by contact with intrusive 

 masses of molten igneous rock ; this caused the calcium carbonate to re-crystallise out as 

 pure calcite, while the impurities contained in the original limestone crystallised out 

 separately as ruby and its associated minerals. The alteration of rocks by contact with a 

 mass of molten igneous material is known to geologists as contact- or thermo-metamorphism ; 

 the results of the process are frequently to be observed in all parts of the world, but, 

 although corundum is often to be found in such altered rocks, fine ruby of gem-quality i>- 

 only rarely met with. Such were the conclusions as to the geology of the district and the 

 mode of origin of the ruby arrived at by Professor Max Bauer, from information and 

 specimens supplied to him by Dr. F. Noetling, and published in a scientific journal in 1896, 

 and in the German edition of the present work. The point of view adopted by Mr. C. 

 Barrington Brown and Professor J. W. Judd,' explained in the paper published shortlv 

 before, and which has already been mentioned, must not, however, be passed over without 

 notice. 



These authors describe the whibe crystalline limestone, which alone contains the ruby 

 and spinel, as occurring in thick bands interfoliated with gneisses. These gneisses are 

 usually of intermediate chemical composition, but sometimes of more acid, and at other times 

 of more basic character ; the crystalline limestones are more intimately associated with the 

 basic gneisses (pyroxene-gneisses and pyroxene-granulites, with pyroxenites and amphibolites). 

 These contain crystals of calcite, and as the proportion of calcite present increases, they 

 merge gradually in the limestones. It is concluded, on these grounds, that the limestones 

 have been derived by the alteration of the lime-felspar in these basic rocks. This felspar 

 (anorthite), being a silicate of calcium and aluminium, would, on alteration, give rise to 

 calcium carbonate and hydrated aluminium silicates, the former being deposited as calcite, 

 and the latter as silica (opal), and various aluminium hydroxides (diaspore, gibbsite, 

 bauxite, &c.). Under other conditions of temperature and pressure these may have been 

 afterwards converted into crystallised anhydrous alumina, that is ruby. 



In the masses of crystallised limestone occurring in situ precious stones are only 

 sparingly present, being found in much greater abundance in the clayey and sandy weathered 

 products of the mother-rock, which lie on the sides of the hills, fill up the bottom of the 

 valleys, and are often overlain by similar detrital material containing no precious stones. 

 This secondary gem- bearing bed consists of brown or yellow, more or less firm, clavey, and 

 at times sandy, material, known to the Burmese as " byon," which may be regarded as the 

 residue after the solution of the limestones by weathering processes. It contains beside 

 ruby, sapphire, and other colour-varieties of corundum, spinel (Tavemier's " mother of 

 ruby "), tourmaline, large fragments of quartz, grains of variously coloured felspars, nodules 

 of weathered iron-pyrites, and other minerals of more or less value, together with fragments 

 of the rocks which occur in situ in the neighbourhood. Sometimes in the river alluvium 

 instead of clayey and sandy material, there are pure gem-sands consisting mainly of minute 

 sparkling grains of ruby. 



The gem-bearing layer lies on a soft decomposed rock of characteristic appearance. 

 When the natives reach this level in their excavations they know that the " byon " extends 

 no further down, and that work at that spot must be abandoned. The " byon " lies about 

 15 to 20 feet below the surface of the floor of the valleys, and is from 4 to 5 feet in thickness 

 though occasionally it may thin off to a few inches. On the sides of the hills the bed of 

 " byon " may be 15 to 20 feet thick, and sometimes as much as 50 feet. 



