M. Daubrde — Formation of Metallic Sulphides. 509 



that, while the interior still shows the lustre and colour of bronze, 

 the exterior consists of a white earthy crust, consisting chiefly of 

 oxide of tin, slightly coloured by traces of copper salts. Thus, by 

 reason of the different chemical affinities of the metals composing 

 the medals, the copper has entered into sulphur combinations, whilst 

 the tin has passed into the state of oxide. This accounts for the 

 mode of occurrence of tin, which is generally found in the state of 

 oxide, even when sulphides, as mispickel, are found associated with 

 it in the same vein. The antimony, notwithstanding its analogies 

 with tin, differs from it in these modern products, as in metalliferous 

 veins, by being invariably in combination with sulphur. 



The silver medals are not altered. 



Geologically short as is the time during which these reactions 

 described by M. Daubree have taken place, yet they supply import- 

 ant results, and afford new evidence of the influence of mineral 

 springs in the formation of metallic sulphides, such as may partly 

 assist in explaining the filling of mineral veins with similar sub- 

 stances. 



Further research has brought to light other facts, as the occurrence 

 of galena, anglesite, mammillated limonite, and iron pyrites. 



The cavities in the bricks used in the conduit for the thermal 

 waters are sometimes found lined with small rhombohedral crystals 

 of chabasite, also some small colourless crystals having the form of 

 rectangular prisms similar to those which occur under analogous 

 circumstances at Plombieres, and which are referred to phillipsite or 

 lime-harmotome. 1 



It thus appears that the zeolitic minerals of the two localities 

 cited, as well as at Luxenil previously described by M. Daubree/ 

 are the result of similar reaction, producing silicates which did not 

 originally exist in the concrete, but which have resulted from the 

 long-continued action of the contents of the thermal waters upon 

 the materials used in the construction of the conduit. It is to be 

 remarked that the water of Bourbonne-les-Bains differs considerably 

 from that of Plombieres, which contains a far less amount of soluble 

 salts, about '3 gramme per litre ; this difference has, however, not 

 affected the formation of zeolites in both. 



M. Daubree concludes by pointing out that thermal springs, flow- 

 ing at limited depths and at slight pressure, produce mineral sub- 

 stances which have not yet been formed in our laboratories. How 

 important, then, must be their effects at greater depths and greater 

 pressure, reacting upon the different rocks which they traverse, and 

 thus produce changes at present veiled to our view, but which should 

 not be overlooked in the consideration of formations which come 

 within the ken of the mineralogist and geologist. 



J. Morris and Thomas Davies. 



1 Comptes Eendus, t. xlvi. p. 1806. (1858.) 



2 Bulletin de la Societe Geologique, 2nd ser. t. xyiii. p. 108. (1860.) 



DECADE II. VOL. 11. NO. X. 33 



