392 Mr. C. B. Brown and Prof. J. W. Judd. [Mar. 7, 



other rocks are found, sometimes broken and waterworn, at other 

 times almost uninjured. 



The study of the extensive series of minerals brought from the 

 ruby mines of Burma is calculated to throw light upon many im- 

 portant scientific problems. 



The association of minerals in the remarkable crystalline lime- 

 stones of Burma is worthy of the most careful consideration. Cor- 

 undum in its various forms of ruby, sapphire, white sapphire, 

 oriental amethyst, oriental topaz, &c. is found associated with red, 

 purple, brown, black and other spinels, the relative proportions of 

 the minerals composed of aluminium oxide and of magnesium alu- 

 minate being very variable. The other minerals present in the crys- 

 talline limestones are zircon (rare) ; garnets (abundant in some 

 places) ; a remarkable blue apatite ; felspars, of many species and 

 varieties (including murchisonite, moonstone, sunstone, &c.), and in 

 every stage of alteration ; quartz (in many varieties, and exhibiting 

 some remarkable peculiarities of crystallisation) ; micas (phlogopite, 

 fuchsite, with muscovite and other secondary and so-called hydro- 

 micas) ; hornblende and arf vedsonite ; augite (sahlite, diopside, and 

 segyrine) ; enstatite (bronzite and hypersthene) ; wollastonite ; 

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

 addition to muscovite and other secondary micas, we find the follow- 

 ing alteration products : Diaspore, margarite, and other clintonites, 

 chlorites, vermiculites, and carbonates. 



It is a noteworthy circumstance that none of the silicates com- 

 bined with fluorine and boron compounds such as topaz, tourmaline, 

 chondrodite and humite, axinite, or datholite have been certainly 

 detected in these limestones. 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 limestone 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 

 c >rundum and spinels are associated with tourmalines and choii- 

 drodites. 



In considering the question of the origin of the corundums 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 011 

 at great depths within the earth's crust. The highly- crystalline 

 calcareous rock, besides containing so many silicates and oxides, is 

 associated in the most intimate manner with pyroxene-gneisses and 



