Magnesile of the Paris Basing 8fc, 293 



f Crystallized quartz 

 Parisian Magnesite ....-< Chert 



t Several varieties of opal (silex resinlte) 

 Magnesite of Salinelle. . Chert 



f Crystallized quartz 



,, . rii. J ■. J Chert (silex come) 



Magnesite of Madrid ..^(.^^l^J^j^^y 



(Several varieties of opal (silex resinite) 

 »» -^ c-Kit ■ S Chalcedony 



Magnesite of Moravia . . J ^hite and green opal (silex resinite) 



f Chert 

 T,, . r v.- J X J Chalcedony 



Magnesite of Piedmont <y^^-^^^^^^ ^^ ^p^i (^Hex resinite) 



(jasper 



Before geology had acquired in principles and facts the 

 precision to which it has now arrived, the presence of mag- 

 nesite in the Paris basin had no other result than that of 

 adding a mineral species to the list of those contained in our 

 country ; but this fact now possesses another interest : it 

 has served to unite observations which were, it may be said, 

 isolated. It informs us that the magnesite beds were depo- 

 sited on the surface of the globe at very diiferent epochs, 

 for some (those of Piedmont) belong to the most ancient 

 sediment rocks, and others (those of Salinelle and Coulom- 

 miers) to the newest sediment (tertiary) rocks ; and yet 

 we see these deposites accompanied by nearly the same 

 geological circumslances. Such a remarkable constancy in 

 the association of silex and magnesia, two bodies between 

 which there is no chemical analogy, will fix the attention of 

 geologists, and may perhaps contribute to shew us the origin 

 of these deposites, as the thermal springs of Italy depositing 

 travertine have pointed out that of the freshwater limestone. 

 It is still apparently from the bosom of the earth that the 

 liquid arose which deposited these rocks; for we find in 

 certain thermal waters traces of all the ingredients of 

 their composition : the mass of water is at present immense 

 in comparison with the matters held in solution ; but these 

 matters exist in it; they are deposited, as M. Berthier 

 has observed at the waters of Vichy, St. Nectaire, &c.* 

 not only separately but nearly in the same order as the 



* Annales de Chiinie et de Physique, t. xix. p. 134. 



