fB 



M. Brocuant on the 



Nevertheless, many characters make me presume that 

 these transition rocks are a little more modern than those of 

 the Tarentaise. 



With regard to the gypsum of Sarran, near Martigny, I 

 could only see Ihe portion that is worked, all the environs 

 being covered by vegetable soil. I know that it is con- 

 sidered as transition gypsum, but I could not obtain the 

 proof of it ; it is very certain that it is not anterior. 



5. Gypsum of Brigg. 



I now come to the two examples in which only I have my- 

 self seen the gypsum very evidently associated with other 

 rocks. 



At Brigg, or rather at about 2000 metres [6562 feet] 

 N.E. from that town, on the left bank of the Rhone, a well 

 characterised bed of gypsum is seen, almost projecting over 

 the bed of the river. Its direction is the same as the valley 

 of the Rhone, nearly E.N.E. and W.S.W. It dips at 43° to 

 the South, exposing its edge to the valley. 



This gypsum is covered by a crystalline whitish grey lime- 

 stone, schistose and mixed with mica. On this limestone is 

 seen another much more coloured, then a spotted blackish 

 schist, that effervesces ; and lastly another schist, that also 

 effervesces, but of a much darker colour, containing insulated 

 plates of mica, and altogether resembling the schists that ac- 

 company the anthracite ; the whole of the thickness of some 

 metres. 



It was then very certain that the gypsum formed the in- 

 tegrant part of a formation, and it might already be conjec- 

 tured to be a transition formation, from the nature of the last 

 mentioned rocks ; this presumption moreover became certain, 

 or at least extremely probable by the other characters of the 

 ground in this part of the valley of the Rhone which belong 

 to this formation ; thus this gypsum has been admitted as 

 transition by naany mineralogists who have observed it. 



