386 Proceedings of Philosophical Societies. [May, 



There is found rather abundantly in a ravine of the Mount 

 d'Or, in Auvergue, fragments of a breccia, the hardness and 

 other external characters of which having led to the supposition 

 of its being of a siliceous nature, mineralogists did not pay much 

 attention 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 v/hich he found that this stone con- 

 tained about 2S per cent, of silica, 27 of sulphuric acid, 31 of 

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

 nearly the sa'ue ingredients as are found in the celebrated ore of 

 Tolfa, which yields Roman alum. In reality, upon treating this 

 breccia from the Mont d'Or, in the same manner as is practised 

 at Tolfa ; that is to say, by breaking it, roasting, and exposing 

 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 roasted, but merely by exposure in a damp situation. 



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

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

 fragments scattered in the ravines were detached, may be disco- 

 vered ; and that quarries may be opened, the working of which 

 cannot but be of advantage. 



M. Cordier regards these sorts of stones as a mineralogical 

 species, consisting essentially of sulphui'ic acid, alumine, and 

 potash. The silica found in it is not essential for quarries of a 

 stone not containing any silica, but all the other constituent 

 principles exist at Montrone, in Tuscany, and yield the same 

 products as that at Tolfa. Those varieties of this species in 

 which silica enters, are easily distinguished by thejelly they form 

 when they are treated in succession with caustic potash and 

 hydrochloric acid diluted with water. 



M. Cordier reduces to this species several volcanic stones, 

 hitherto vaguely designated by geologists by the general deno- 

 mination of altered lava. 



Some country people in the department of the Lot, allured by the 

 hope of finding pretended treasures, which are said to have been 

 formerly buried by the English in certain caves in the iieighbour- 

 hood of Breugue, have penetrated into these cavities, and having 

 dug into and enlarged' some crevices which they found at the 

 bottom of them, they have discovered a deposition of bones, 

 some of which belong to horses, others to that species of rhino- 

 ceros, of which so large a quantity of fossil bones have been 

 found in Siberia, Germany, and England ; others again to a 

 species of cervus not at present known to exist, and the horns of 

 which have some slight analogy with those of a young rein-deer. 



Guettard found a great number of these horns in the neigh- 

 bourhood of Etampe. 



