36 



LA TOUCHE : GEOLOGY OF NORTHERN SHAN STATES. 



lapis-lazuli ; fibrolite ; scapolite ; with graphite and pyrrhotite. In addition 

 to muscovite and other secondary micas, we find the following alteration pro- 

 ducts : — Diaspore, margarite and other clintonites, chlorites, vermiculites, and 

 carbonates. 



" It is a noteworthy circumstance that none of the silicates combined with 

 fluorine and boron compounds — such as topaz, tourmaline, chondrodite and 

 humite, axinite, or datholite — have been certainly detected in these limestones. 1 

 Beryl (aquamarine) and danburite have been said to occur in the ruby earths, 

 but there is reason for doubting the correctness of the statement. The lime- 

 stone which, in the association of minerals found in it, most closely resembles 

 the rock of Burma, is the remarkable white limestone of Orange County, 

 N. Y., and Sussex County, N. J., but in the American rock the corundum 

 and spinels are associated with tourmalines and chondrodites. 



" In considering the question of the origin of the ccrundums and spinels 

 of Burma, there are several very important facts to be borne in mind. The 

 gems, when found in situ, always appear to occur in the limestone, and 

 this limestone is of a very remarkable character. There are no facts which 

 point to the conclusion that the limestone was originally of organic origin, 

 but many circumstances suggest that it may have been formed by purely 

 chemical processes going on at great depths within the earth's crust. The 

 highly-crystalline calcareous rock, besides containing so many silicates and 

 oxides, associated is in the most intimate manner with pyroxene -gneisses and 

 granulites containing anorthite, and with various pyroxenites and amphibolites. 

 The lime felspars and lime-soda felspars of these rocks show the greatest 

 tendency to undergo change — passing into scapolites by the process known as 

 ' werneritisation,' and eventually giving rise to the separation of calcium car- 

 bonate and hydrated aluminium silicates. That from the last mentioned 

 salts the hydrated oxides of aluminium (diaspore, gibbsite, bauxite, etc.) may 

 be separated has been shown by the studies of Liebrich and others, while 

 the conversion of these substances into the anhydrous aluminium oxide has 

 been shown to take place by H. St. Claire Deville, Stanislas Meunier, and 

 others. 



" Of still greater interest than the question of the origin of the corundums 

 and spinels are the problems connected with the remarkable changes that 

 these minerals undergo in deep-seated rock masses. The rubies of Burma, 

 when found in situ in the limestones, are usually seen to be enveloped in a 

 mass of materials produced by the alteration of their superficial portions. 

 Nearest to the unaltered gem is a zone of diaspore — the hydrated aluminium 

 oxide — and this is found to pass insensibly into various hydrous aluminous 

 silicates — margarites and other clintonites, vermiculites, muscovites, kaolinites, 

 etc. While, in some instances, the corrosion of the rubies appears to have 

 gone on in a seemingly irregular manner, in the majority of cases a very 

 definite mode of metamorphosis may be detected by the study of the various 

 examples. There are evidently certain planes of ' chemical weakness ' (analo- 

 gous to the cleavage planes, gliding planes, and other direction k of physical 



1 In the crystalline limestone of the Manwe-Naniazeik ruby tract in the Kacbin Hills 

 chondrodite and tourmaline are both found, according to Dr. Bleeck. (Rubies in the 

 Kacbin Hills ; Records, Geol. Surv. Ind., Vol. XXXVI, Pt. 3, p. lt>7). 



