320 DESCRIPTION OF THE TIN VEINS 



made to a greater depth than three feet ; and hence we are unable 

 to estimate the probable value of the ore which may be obtained 

 by mining. Tracing the principal vein to the southward, we lost 

 sight of it in the valley ; but on the rising ground beyond we 

 again found Ihe ore, with its usual associated minerals. This 

 locality is one fourth of a mile south of the principal vein, and in 

 the direction of its course. 



On revisiting this locality, I discovered several new veins of 

 compact oxide of tin, and obtained ninety-eight pounds of the 

 ore, which yields on the average forty per cent, of tin, while the 

 clean ore freed from the rock yields seventy-three per cent, of metal. 

 By a single assay of this ore I obtained from twenty-one ounces 

 of rock and ore, taken just as it was blasted out, eleven and a 

 half ounces of pure tin. 



Remarks on the Theory of the formation of Tin Veins. 



M. Daubree^Ingeneur des Mines, has published some interest- 

 ing remarks on the theory of tin veins. (Annales des IMines, 

 tome XX, 4me li\Taison July and August, 1841.) 



He considers the origin of the oxide of tin in veins to have 

 arisen from the volatiHzation by heat of the fluoride of tin from 

 the interior of the globe ; and that, as the fluoride, thus sublimed 

 into crevices of the rocks, was decomposed by water or earthy 

 bases, the oxide of tin was deposited on the surfaces of the fis- 

 sures, and the veins became filled with the ore. 



In order to prove the presence of fluorine, he cites the fact of 

 the constant occurrence of fluor spar in tin mines, and also re- 

 gards the investing layers and crystals of quartz as formed by the 

 sublimation of fluorides. He also supposes, that the combina- 

 tions of boron and fluorine were raised in vapor, and that the oc- 

 currence of tourmaline in all tin veins is a proof that boron was 

 present at the time of their formation, that mineral containing 

 boracic acid. Mica also, containing fluoric acid, is a frequent 

 associated mineral in tin veins. 



It is interesting to obscn'c the remarkable agreement of the 

 facts noticed at Jackson with those cited by M. Daubree. It is 



