ancient Gypsum of the Alps. 83 



that have spoken of this gypsum, I have not been able to 

 find any direct or positive obs&rvation. M. Lardy, an able 

 mineralogist, a notice by Avhoih is seen in a preceding part 

 of these Annales,* on the gypsum of the Val Canaria, does 

 not mention any foreign bed in it; he admits, as I have 

 above said, that no gypsum is met with at a certain height ; 

 which is the more remarkable as he joins in the received 

 opinion of the gypsum being primitive ; but he rests this 

 only on the relations that he thought he saw between the 

 direction and inclination of the gypsum beds and those of the 

 mica slate beds, relations which I am far from admitting, on 

 account of the irregularity noticed above in the stratification 

 of the gypsum. He concludes from these relations that the 

 gypsum there forms a thick bed under the mica slate. 



It is rmpossible for me to admit this opinion ; it appears 

 to me on the contrary, evident, that if the gypsum occu- 

 pying all the lower part of the valley was included in the 

 mica slate, or ivas covered by it, that it must, from the 

 disposition of tlte mica slate beds and their escarpments, be 

 found in some part of the heights ; and it is from its total 

 disappearance, beyond a certain level, that I found my 

 conclusion that the gypsum is not contemporaneous, but pos- 

 terior to the mica slate, and that there is no reason for con- 

 siderihg it primitive. 



It now remains to determine to what formation it belongs. 

 But as it is not covered by any other rock, it is impossible 

 Xo decide this question rn a positive manner : I shall here- 

 after throw out a conjecture that appears to me very pro- 

 bable. 



I shall here only add that the formation of the gypsum 

 appears to be later even than the hollowing out of the Val 

 Canaria. The contraction of that valley at its mouth, and 

 the form of the gypsum mass, which aifords a tolerably even 

 surface, present more than in other places the idea of a 

 deposit in a basin, or as has been said in a lake ; an idea 



* I have not translated this paper, M. Brochant's description lender- 

 ing it unnecessary. (Trans.) 



F 2 



