60 PROF. T. G. BONNET ON THE [Feb. 1903, 



Larsine the magnetite (rarely ferrite-stained) sometimes forms little 

 patches, also pierced by flakes, which occasionally give fairly bright 

 polarization-tints, and a slightly oblique extinction (measurement 

 is difficult), and thus are probably actinolite. The specific gravity 

 of the one rock is 2*49, of the other 2-54 : both a little light for an 

 average serpentine, which, however, is probably due to their cracked 

 condition. 



The ' intermediate ' specimen, from the edge of the mass at the 

 Pilon Licone, consists also of serpentine and magnetite, but the flakes 

 of the former are sometimes rather larger than those above described, 

 though occasionally little patches occur, composed of exceedingly 

 minute fibres, thus appearing almost isotropic. The possibly actino- 

 litic mineral is also present, though small in size, and is associated 

 in one place with calcite, perhaps slightly dolomitic. In one part of 

 the slice augite is plentiful in associated grains, separated by minute 

 irregular strings of the ordinary serpentine. The specific gravity of 

 the specimen is 2-77. 1 The other two specimens, from the Filon 

 Larsine, are still more ' intermediate ' in character. Both present 

 to the unaided eye a granular structure — serpentine rather irregularly 

 mottled' with magnetite : sometimes one, sometimes the other 

 dominating. The specimen broken from the entrance of a gallery 

 and within half a yard, or possibly less, of the pure ore has a 

 specific gravity of 3-54 ; the other one was selected from the ' tip ' 

 as a good sample of the intermediate rock, and its specific gravity 

 is 3 # 73. The microscope shows both these specimens to consist of 

 serpentine (in rather smaller flakes than before, but in the second 

 case with a fair amount of the brighter coloured variety) and of 

 magnetite, more abundant and much of it in bigger grains. Slight 

 indications of pressure are perceptible, but in all other respects the 

 rock bears such a close resemblance to the cumberlandite, so 

 admirably described and figured by Prof. Wadsworth, 2 that it is 

 needless to do more than add another locality to his list. 



Two points, however, in these Cogne specimens call for some 

 further notice : the history of the rock and the relation of the 

 magnetite-mass to the normal serpentine. Whether the pressure 

 acted before or after the conversion of the olivine into serpentine 

 is not easily determined. We do not even know the age of the 

 original peridotites. The Alpine serpentines are intrusive in the calc- 

 mica-schists and the green schists (which sometimes, at any rate, 

 are intrusive in the others), and seem to be restricted to the 

 crystalline series. 3 The grains of magnetite in the rock-slices 



1 It would have been easy to have obtained one richer in magnetite, but 

 this was selected because it approached nearer to a normal serpentine and 

 bordered on the augite- Tein, mentioned above. 



2 ' Lithological Studies ' Mem. Mus. Comp. Zool. Harvard, vol. xi (1884) pi. i, 

 figs. 5 & 6, and pi. ii, figs. 1, 2, & 3. In these the olivine generally remains, 

 but in fig. 6 it is replaced by serpentine. The specimen with some others are 

 described (pp. 75-82), and their specific gravity ranges from 3*55 to 406. 



3 There is a possible exception in the Brenner district (Pfons), but I failed 

 to find conclusive evidence as to the relation of the serpentine to the Trias. 



