Magnesite of the Paris Basin, S^c. 291 



rid, possesses the same tenacity, the same hardness, the same 

 lightness, the same superficial roseate tint, as those of Cou- 

 lommiers and Salinelie, It is equally composed of 23 parts 

 of magnesia, 53 of silex, and 20 of water; it is accom- 

 panied, like ours, by chert (flint ?), which also passes 

 into its mass, by common opal (silex resinite), by chalce- 

 dony, by crystallized quartz, and calcareous spar altogether 

 resembling those of our siliceous limestone. It affords, 

 certainly, no organic remains ; but we know that these re- 

 mains are rare in the siliceous limestone of the Paris basin, 

 of which our magnesite forms a part ; lastly if it appears to 

 differ by its position on a saliferous gypsum, much more 

 ancient than our gypsum, and calcaire grossier, it is not 

 covered by any rock which appears more ancient than the 

 latter, and it is like them in horizontal beds. 



If from Spain we transport ourselves to Italy, to the foot 

 of the Piedmontese Alps, we shall find, at a short distance 

 from Turin, the serpentine hills of Castellamonte and Baldis- 

 sero, traversed in every direction by veins of magnesite which 

 is tenacious yet plastic, light, and with that roseate superficial 

 tint which we have noticed in the preceding magnesites. 

 Its principal or fundamental and characteristic composition 

 appears to be still the same, i. e. of magnesia, silex, and 

 water. Here however we have carbonic acid, which seems 

 to indicate a different chemical species ; but its geological 

 circumstances are still the same. I have already noticed 

 them in my memoir on the geological position of the serpen- 

 tines, where I have given a figurative section of them. 



The mineral no longer occurs in horizontal beds, or no- 

 dules interposed in the beds, but in numerous veins, uniting 

 in every direction in the midst of the serpentine ; chert, 

 common opal, and jasper, presenting many varieties of tex- 

 ture and colours, are constantly and intimately united with 

 it, as at Coulommiers and Salinelie. They have been 

 formed even in the midst of the magnesite. This circum- 

 stance of geological association is then remarkably constant, 

 even when the geological position has no longer the same 



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