288 M. Brongniart on Me 



basin ; now, it is remarkable, that we find the magnesite 

 with ail the circumstances -which accompany it in that part 

 of the Paris basin where it is most pure. 



Magnesite has long since been observed at Salinelle near 

 Sommieres, in the department of the Gard, between Alais 

 and Montpellier ; but its position has only been determined 

 a few years since, by the description M. Marcel de Serre 

 has published of it. 



It is therefore solely to the remarkable analogy of this 

 position with that of Coulommiers that I wish to call the at- 

 tention of naturalists. The magnwsite of Salinelle is schistose 

 like that of Coulommiers ; it possesses the same colour, ap- 

 proaching grey with a roseate tint, with the same tenacity ; 

 it absorbs water in the same manner; it is composed of the 

 same ingredients, i. e. 20 parts of magnesia instead of 24, 

 51 of silex instead of 54, and 22 of water instead of 20. It 

 will be acknowledged that it is difficult to meet with more 

 resemblance between uncrystaliized minerals, which occur 

 at more than 100 leagues from each other, and if the mine- 

 ralogical species cannot be here determined by the form, it 

 is sufficiently so by the composition : the analogies drawn 

 from its associated minerals, and its position are the same ; 

 it is mixed with nodules of chert (silex come) which resem- 

 ble our menilite; it is accompanied and covered by marly 

 limestone containing fresh water shells, consequently it be- 

 longs, w ilh that of the Paris basin, to a calcareo-siliceous 

 fresh water formation. 



But magnesite, i. e. this stone essentially composed of 

 magnesia, silex, and water, occurs in many other places dis- 

 persed over the surface of Europe, and consequently placed 

 at great distances from each other. Sometimes we are ac- 

 quainted with its mode of occurrence, and then we know 

 that it is very diiferent from that I have above described ; 

 sometimes we are ignorant of it, or at least we do but pre- 

 sume it; but in all these places and in all these positions 

 we ahall see the magnesite to occur accompanied by the 

 same mineralogical characters and the same geological cir- 



