﻿698 PROF. T. G. BONNE Y AND MISS C. RAISIN ON THE ["Nov. I905, 



a granular structure, and consists of a pale augite (the more 

 abundant), fairly clear, though setting up a diallage- cleavage, and 

 a very clean serpentine which often produces little effect on 

 polarized light, but sometimes gives low tints, revealing traces of 

 a platy cleavage and generally extinguishing obliquely with it. 

 This fact, the residual granules of augite in the serpentine, and the 

 way in which the latter occasionally seems to soak like water into a 

 grain of the former, justify us in regarding the one as an alteration- 

 product of the other. 



Miss Raisin obtained a rather remarkable pyroxenic serpentine from 

 the Felleringenkopf in the Southern Vosges. In the hand-specimen 

 it appears to be a dark serpentine, 1 mottled with a paler green 

 (perhaps merely the thin edges of fractures), and spotted with fairly- 

 numerous pale brass-yellow to whitish grains with an undulating 

 platy cleavage. The microscope shows the following minerals : — 

 (a) grains of an iron-oxide (not abundant) ; (b) grains with a rather 

 wavy parallel cleavage, indicated by granules or short belonites of 

 opacite; polarization-tints whitish to a distinct dull blue; extinction 

 probably straight, but difficult to measure because of curvatures ; 

 (c) a dusty-brown fibrous mineral, alternating in flakes with, and 

 apparently passing into, the last one, and giving, when this can be 

 seen, marked pleochroism and rather bright polarization-tints, with 

 straight extinction ; (d) a colourless mineral associated with small 

 grains of a granular, or fibrous granular, light honey-brown mineral, 

 which is probably an augite, aud seems to pass into an almost 

 amorphous aggregate acting very feebly on polarized light. No 

 structure characteristic of olivine occurs in the slice and, notwith- 

 standing the megascopic aspect of the rock, two varieties of enstatite 

 with some augite seem to be more probably its original constituents. 

 Bent cleavages and other irregularities in this specimen suggest 

 slight mechanical disturbance. 



A slice of another rock from the same locality contains augite 

 in small grains or prisms parted by very narrow films of appa- 

 rently-amorphous serpentine. These are obviously residues of 

 larger grains, which occasionally suggest slight mechanical dis- 

 turbance. We also find minute flecks scattered about the slice, 

 with little granular fibrous and rather dirty-looking spots. These, 

 when highly magnified, prove to be augite, and occur like islands 

 in the serpentine which (with some opacite and grains of iron- 

 oxide) occupies most of the slice, and produces no sensible effect 

 on polarized light. Thus augite, which now is the only anhydrous 

 silicate recognizable in the rock, seems to have been formerly very 

 abundant. 



In a third specimen from this locality the greater part of 

 the slice suggests, by the disposition of the opacite, the former 

 presence of an olivine ; the structure of the serpentine is minute 

 and its action on polarized light rather feeble, but it seems 

 locally to become irregularly fibrous. Here and there spots occur 

 free from opacite, but containing numerous small fibrous flakes of a 



1 Not unlike the black serpentine of the Lizard, the Apennines, Corsica, etc. 



