488 



THE GEOLOGIST. 



lised in very hard hexagonal laminae ; but it was not emerald, for by- 

 analysis it was proved deficient in silica. 



It will be perceived from what has just been related, that fluoride 

 of aluminium decomposes silica to form fluoride of silicium and stauro- 

 tide. And, also, that in the same manner, fluoride of silicium in con- 

 tact with alumina gives fluoride of aluminium and staurotide. This is 

 the reason why our smelting crucibles and other metallurgical apparatus 

 are often entirely transformed into a rough mass of crystals, almost all 

 of which consist of the mineral species staurotide. The preceding 

 observations explain also how volatile fluor-compounds in the presence 

 of argillaceous substances may become the means of obtaining crystals 

 of substances which are perfectly insoluble or infusible at the tem- 

 peratures at which these fluor-compounds operate. This remarkable 

 influence of metallic fluorides in the production of crystallized mineral 

 species must have played a certain part in nature — more particularly 

 in the production of crystallized minerals in lodes and veins. At least, 

 such is the opinion of M. H. Deville ; and M. Daubree seems already 

 to have arrived at this conclusion in his beautiful memoirs on the 

 metallic fluorides. At the end of their paper, Messrs. Deville and 

 Caron state that they have likewise artificially obtained rutile, or 

 titanic acid, an interesting mineral species, in decomposing a fusible 

 titanite by silica. Titanite of protoxide of tin was preferred for this 

 experiment. During the operation, the authors remarked dissolved in 

 the metallic tin, a brilliant substance, crystallised in wide metallic 

 laminae, easily separated from the tin by dissolving the latter in hyro- 

 chloric acid, and which turned out to be an alloy of iron and tin, con- 

 taining equal proportions of each. 



It was stated several months ago, that the immense work of a tunnel 

 under the Alps between Modane and Bardoneche had commenced. We 

 have now to record some interesting facts, which might perhaps never 

 have been discovered but for the peculiar methods employed in this 

 colossal operation. The crest of the mountain attains so great a height 

 that the sinking of shafts, which is generally done in order to begin 

 boring at several points at once, was in this case out of the question. 

 Hence the tunnel could only be worked at its extremities, so that the 

 labour by the ordinary process of working could not be accomplished in 

 less than thirty-six years ! Then, how was a depth of gallery of one or 

 two miles, or more, and having but one orifice, to be aired These 

 were very serious obstacles. 



MM. Elie de Beaumont and Angelo Sismonda having examined the 

 mountain geologically between Modane and Bardoneche, found it com- 

 posed of micaceous sandstones and schists, quartzite, gypsum, and lime- 

 stone, all easy to blast, the quartzite alone excepted ; but the stratum 

 of this is not likely to be very thick. The other difficulties alone, 

 therefore, remained, and these were at length overcome by three 

 Sardinian engineers, MM. Sommeiller, Grattone, and Grandis, who 

 proposed to turn the abundance of water, for which the locality is 

 remarkable, to account by applying it to a peculiar system of perfora- 

 tion and ventilation, which we will now endeavour to explain. The 

 first apparatus imagined by these gentlemen consists of an hydraulic 



