ancient G?/psum of the Alps. 79 



6. Gypsum of Cogne. 



The position of this gypsum, noticed as primitive by M. 

 Daubuisson, who discovered it in 1807, has been described 

 by him in a notice inserted in the Journal des Mines, No. 

 128, p. 161. I shall here content myself by repeating its 

 principal characters, and adding some original observations. 



This gypsum is found on a ridge of rock of about 2,400 

 metres [7874 feet] elevation ; it does not itself form 

 the ridge, which is calcareous, but is a little below. The 

 beds are nearly horizontal. The gypsum is worked to the 

 depth of about two-thirds of a metre ; but the floor of the 

 bed has not been discovered, being concealed by the de- 

 bris of which this slope is covered ; the roof is a limestone 

 that is a little crystalline, blueish grey, and very schistose 

 from a mixture of talc. This rock has not a thickness up 

 to the surface of more than a metre or metre and a half 

 [about 3 feet 3 Inches to 5 feet] ; it is full of crevices. 



The workings cover a space of from six to seven metres 

 [about 19| to 23 ft.] in length, and as the gypsum is quarried 

 solely for the use of the inhabitants of the valley, it is rarely 

 worked. Mounting the ridge of rock, debris are only found, 

 and no out-crop of the gypsum, and the principal inhabi- 

 tants have assured me that there did not elsewhere exist the 

 slightest trace of it throughout the valley. 



Among the debris covering the slope much schistose lime- 

 stone is met with, and also numerous fragments of quartz 

 slightly micaceous. Notwithstanding the singularity of this 

 position, it would be difficult to refuse admitting the con- 

 temporaneous origin of the gypsum and limestone; but I 

 shall remark : 



1. That this schistose limestone bears, from its colour, 

 its mixture of talc, and all its other characters, a great re- 

 lation to that so abundant in the Tarentaise, and also to that 

 covering the gypsum at Brigg. 



Those accustomed to the study of rocks know, that there 

 exists between the members of the same formation an assem- 



