68 M. BnocHANT on the 



from some characters of position, that the well recognized 

 nodules were of an origin little anterior to that of the gyp- 

 sum. 



These decided calcareous nodules occur abundantly in 

 the gypsum of Pesey, also in that of Brides in Savoy. Those 

 of St. Leonard and Bex afford it also. They are perfectly 

 decided in the two first places. 



2d. Mica or rather talc. It is only found in two of the 

 above mentioned positions ; at the Val Canaria and Brigg. 

 At the Val Canaria, mica is disseminated in an uniform man- 

 ner in the rock, sometimes in little Insulated plates of a 

 greenish yellow, at others, a little fibrous in small groups. 

 Even in the midst of the gypsum some yellowish masses are 

 observable, that are principally composed of mica; they also 

 contain gypsum, but it is as it were dissolved in the midst 

 of the mica, the colour of which it has taken, and to which 

 it serves, it may be said, as a paste. These masses afford 

 shining surfaces, when broken, in which the mica is fibrous. 



I have here used the name mica, because the gypsum of 

 that locality has bieen generally noticed as micaceous ; but 

 I should observe, that it possesses many of the characters of 

 talc, that it is one of those numerous passages, recognized 

 between these two substances, which have made their future 

 union into one mineralogical species probable, passages of 

 which the rocks of the Alps have afforded me many ex- 

 amples. 



At Brigg, the talc is more decidedly shewn. It is not 

 disseminated throughout the mass of gypsum as at the Val 

 Canaria ; it forms plates or rather a sort of varnish on the 

 surface of the laminae of the rock which is a little schistose. 



Its colour is a silvery greenish white ; it is slightly fibrous. 

 This presence of mica and talc in these two gypsums, joined 

 with the identity of colour of the gypsum itself, is cer- 

 tainly not sufficient to assign them the same geological 

 origin ; nevertheless, it cannot be denied that there exists 

 between them a sort of resemblance, which is the more re- 

 markable and extraordinary, as the last of these gypsums 

 (that of Brigg) is referred to the transition series by many 



