7t Breccia vj Kloni d Or. 



the lead in that case, when exposed on the Lupel, remains tar- 

 nished, and exhibits on the surface small quantities of oxide of 

 tin. 



When tin is alloved with some per cents, of copper, this last 

 metal may be distinguished on the cupel by the rose-red colour 

 which makes its appearance. — {Ann. de Chim. el de Pliys. xii. 

 342.) 



BRECCIA OF MONT d'OR. 



There are found rather al)undantiy in a ravine of Mont d'Or, 

 in Auvergne, fragments of a breccia, the hardness and other ex- 

 ternal characters of whi'.-h having led to the supposition of its 

 being of a siliceous nature, mineralogists did not pay much at- 

 tention to it, except on account of some particles of sulphur 

 which it sometimes contains in small cavities. 



M. Cordier, having submitted this breccia to different trials, 

 found that it yielded by heat a notable proportion of sulphuric 

 acid ; and upon this important indication he proceeded to make 

 a complete analysis of it, by which he found that this stone con- 

 tained about 28 per cent, of silica, 27 of sul|)huric acid, 31 of 

 alumine, 6 of potash, and a little water and iron. These are 

 very nearlv the same ingredients as are found in the celebrated 

 ore of Tolfa, which yields Roman alum. In reality, upon treat- 

 ing this breccia from Mont d'Or in the same manner as is prac- 

 tised at Tolfa, that is to say, by breaking it, roasting, and ex- 

 posing it to a moist air, from 10 to 20 per cent, of very pure 

 alum was obtained from it ; and this breccia even yielded alum 

 without being roosted, but merely by exposure in a damp situa- 

 tion. 



It is probable, from the researches made upon the spot by 

 M. Ramond, that, with some pains, the beds from which the 

 fragment" scattered in the ravines were detached, may be disco- 

 vered ; au'l that quarries maybe opened, the working of which 

 camiot l.ut l)e of advantage. 



M. Cordier regards these sorts of stones as a mineralogical 

 species, consisting essentially of sulphuric acid, alumine, and 

 potash. The silica found in it is not essential for ijuarries of f^ 

 stone not containing any silica ; but all the other consistent prin- 

 ciples exist at M('ntrone, in Tuscany, and yield the same pro- 

 ducts as that at Tolfa. Those varieties of this species in which 

 silica enters, are easily distinguished by the jelly they form when 

 they are treated in succession with caustic potash and hydror 

 chloric acid diluted with water. 



M. Cordier reduces to this species, several volcanic stones, 

 hitherto vaguely designated by geologists by the general denor 

 nination of altered lava, 



MEDALLIC 



I 



