74 M. BiiovuAJfT on the 



consequently posterior to the transition limestone, since I 

 have elsewhere shewn that the metalliferous rock of Pesey, 

 M hich is an argillo-steaschist, was of the same formation as 

 all the limestone of the Tarentaise. 



In order more fully to assure myself of it, I searched the 

 points of the adit level, and the excavations that communi- 

 cate with it, which led from the rock to the gypsum, in order 

 to observe their superposition ; but the wood work and the 

 decomposition of the two rocks prevented me from obtaining 

 any decisive result. I remained therefore in the same un- 

 certainty with regard to my first presumption, which never- 

 theless always appeared to me the most probable opinion. 



Lastly, while following the workings the miners met with 

 gypsum, and in order to re-discover the metalliferous rock 

 they were obliged to abandon the principal gallery and sink 

 a shaft. I observed the spot where the metalliferous rock 

 was in contact with the gypsum ; the latter was not dis- 

 tinctly stratified, and the laminae of the metalliferous rock 

 were cut very obliquely ; so that their mode of association 

 was still doubtful. 



To clear this up, I requested M. Schrieber, at that time 

 director of the practical school and the mine, to drive a 

 transverse gallery in the metalliferous rock, precisely at its 

 junction with the gypsum. 



This gallery (which, having geological research for its 

 principal object, was named the geologist's gallery), was 

 executed, and driven the distance of twenty metres [about 

 65 feet 6 inches] ; it furnished me with an opportunity of 

 judging decidedly on the position of the gypsum with regard 

 to the metalliferous rock. 



It was found that the gypsum was only vertically placed 

 against the edges of the beds of the metalliferous rock, 

 which were cut vertically. One of the sides of the gallery 

 was a perpendicular wall of very even gypsum, the other 

 presented the edges of the beds of the rock cut a little 

 obliquely to their planes ; it then appeared to me evident 

 that the gypsum was a later formation than the metalliferous 



