Vol. 59.] 



MAGNETITE-MINES NEAR COGNE. 



57 



ascending to the mine, crossing, once at least, a little green schist. 

 At the mine itself the mass of ore has been quarried into a cliff 

 (fig. 2), its ends being hidden by spoil-bank ; and the greater part, so 

 far as we could see, consisting of a pure magnetite, perhaps 60 feet 

 thick at the middle. 1 It is capped by brownish calc-mica-schist, 

 the junction being very clear and sharp, though inaccessible. Tn 

 this mass were three or four excavations, the largest, about 20 feet 

 high and 18 feet wide at the entrance, expanding as it descended ; 

 but we could not enter it or the next in size, as they were filled with 

 water in which masses of ice were floating. The jointing of the 



Pig. 2. — The Filon Licone. 



[Rough sketch of the magnetite overlain by calc-mica-schist in the quarry-cliff: 

 the height is rather exaggerated in proportion to the breadth.] 



1 = Calc-mica-schist ; 2 = Magnetite (the dotted lines indicate mines) ; 

 3 = Part of an Alp. 



magnetite, both in the cliff-face and in the loose blocks, reminded 

 me of a serpentine; and a slight steatitic film was occasionally 

 perceptible on the brown joint-faces. 2 I then scrambled along the 

 spoil-bank to the more western end of the mass of ore, where it 

 began to disappear beneath the turf. Here I found that the rock 

 consisted of a granular mixture of magnetite and serpentine, which 

 showed some signs of pressure and was slightly veined with a pale 

 yellowish-brown variety of augite (? mussaite). An examination of 

 this part convinced me that the ore and the rock were not sharply 

 divided, but that the one passed, though rather quickly, into the 

 other. About a furlong away in the same direction (the intervening- 

 part being masked by debris from above and by turf) a rather similar 

 rock crops out from beneath the calc-mica-schist (fig. 3, p. 58). 



1 M. Parran, Bull. Soc. Geol. France, ser. 3, vol. ii (1874) p. 257 gives the 

 maximum thickness as from 25 to 30 metres, and the length of it as 150 metres. 



2 A few days before, we had seen a heap of blocks near Cogne, and on 

 approaching them were at once struck with the resemblance. On them also 

 we noticed the brown steatitic film. 



