Revieics- — A. Daubree's Experimental Geology. 423 



that the accompanying elements, besides silicon, are boron and 

 fluorine, and frequently phosphorus and arsenic, forming combina- 

 tions which cannot be explained by the mere chemical analogies 

 of these different elements, as is the natural association of iron with 

 manganese, or cobalt with nickel. These observations have been 

 supplemented in a recent contribution to the Quart. Journ. Geol. 

 Soc. by Dr. Le Neve Foster, who gives some very interesting details, 

 especially as to the fact of lodes, containing from one to three per 

 cent, of cassiterite, themselves consisting of schorl rock, which he 

 describes as a matted mass of fine needles of schorl in a ground mass 

 of quartz, with granules of cassiterite scattered through it, or ar- 

 ranged in little strings and veins. From these considerations it may 

 be gathered that fluorine was the agent which performed at once 

 the part of carrier and of mineralizer, thus discharging the task 

 allotted to sulphur in the plumbiferous (sulphuretted) group. 



Fluoride of tin is a compound stable at high temperatures, and in 

 all probability the tin came up as fluoride from the general reservoir 

 of the heavy metals. Boron too has a tendency to combine with 

 fluorine, and fluoride of boron being volatile would also ascend. 

 In the artificial preparation of cassiterite, effected by M. Daubree 

 as long ago as 1841, not having conveniences for the employment of 

 fluorides, he brought together in a porcelain tube the vapour of 

 bichloride of tin and steam at a temperature below 300° C. Small 

 but well-formed crystals resulted, having a density of 6-72, and 

 adhering closely to the sides of the tube. Similarly, by employing 

 perchloride of titanium, he obtained small crystalline grains of 

 titanic acid. The artificial production of apatite was effected by the 

 action of perchloride of phosphorus, first on caustic lime and after- 

 wards on chalk, the result being a true chlor-apatite. In these 

 operations some chloride of silicon was formed at the expense of 

 the porcelain. Thus he argues, that if the vapours of stannic 

 chloride and fluoride, which appear to have formed the stanniferous 

 deposits, were accompanied by perchloride of phosphorus, this latter, 

 when encountering lime in the enveloping rocks, must have formed 

 apatite accompanied by fluor spar. 



Still referring to this subject, M. Daubree, whilst apologizing for 

 introducing his own work as that of a geologist rather than of a 

 chemist, mentions that, seventeen years after these experiments 

 (viz. in 1850), Deville pi'oduced corundum by means of volatile 

 metallic fluorides re-acting on oxidized compounds, and that by 

 means of fluoride of titanium Hautefeuille reproduced the three 

 forms of titanic acid. 



The sulphuretted group, being the one in which the majority of 

 metals occur, is not dealt with generally, but M. Daubree points out 

 the existence of analogous products of recent formation in warm 

 springs, such as those of Bourbonne-les-Bains. An abstract of the 

 author's paper in the " Comptes Eendus " for 1875 has already 

 appeared in this Magazine. Bourbonne-les-Bains is not the only 

 place where Roman coins have yielded metallic sulphides, but tnere 

 the circumstances seem to have been peculiarly favourable, and 



