﻿Vol. 6 1.] MICROSCOPIC STRUCTURE OF SERPENTINE. 711 



except as mementos or samplos of anything unusual, he brought 

 away a bit not so big as his thumb from the Riffelhorn. He lias 

 forgotten the exact locality, but thinks that it probably came from 

 rather low down on the northern face of tho peak. A short time 

 ago, as it seemed a little different from his other specimens, he had 

 it sliced, and found it to be not only practically unaffected by pres- 

 sure, but also to exhibit most distinctly the peculiar mesh-structure 

 of serpentine derived from olivine, and to contain a little altered 

 enstatite. The replacing mineral in the ' strings ' (clotted occasion- 

 ally with black iron-oxide) affords low polarization-tints in the first 

 order (rarely reaching palo yellow) and that in the interstices is 

 almost inert, as it also is in the replaced enstatite. The occurrence 

 of this saxonite, in such close association with an augitite, shows 

 that at presont we could not safely claim the latter rock as the in- 

 variable parent of a fissile serpentine. 1 



In a slaty serpentine collected ' a short distance above Verrex, 

 Val d'Aosta,' the iron-oxide indicates great crushing and the bulk 

 of the slice consists of a felted foliated mass of the usual mica- 

 like mineral with low polarization- tints, though it is large enough 

 in places (about -025 inch long) to give the higher colours if they 

 depended on size alone. The slice also contains a few small streaks 

 (probably formed in cracks) of a rather mica-like colourless mineral 

 in stoutish flakes (not exceeding # 01 inch) which show palo-yellow 

 (inclining to buff) polarization-tints and give straight extinction. 



A still more slaty serpentine (about a quarter of an inch thick) 

 comes from near the Col de Vallante (Viso district). 2 It is a felted 

 foliated mass (with slight ' rucking' or 'stepping') of rather minute 

 flakes, and a little crushed iron-oxide, which shows a faint tinge of tho 

 usual pleochroism, and affords, when placed at an angle of 45°, as 

 mentioned above, fairly-bright polarization-tints occurring streakily 

 — the clear yellow of the first order to the blue of the second, rather 

 bright in one part. Some longer flakes occur, and a little patch of 

 another mineral which gives straight extinction and low polarization- 

 tints — a pale greyish- buff — (? a form of chlorite). A less fissile 

 specimen, from rather nearer the Col so far as tho collector 

 remembers, is a little hard, consists of ' antigorite ' of both tints, 

 rather foliated, together with powdered magnetite and some flakes 

 (pale green and very feebly pleochroic, having a little opacite 

 between the cleavages) which reach the blue of the second 

 order. 



1 At the same time, after examining a rather numerous collection of fragments 

 which Miss Raisin brought some years ago from this district, I think that the 

 bulk of the rock, whether slaty or not, represents the augitic group. [T. G. B.] 



A specimen in Miss Raisin's collection, sliced since these words were written, 

 from a block on tho right bank of the Zinutt Glacier, beneath the Matterhorn, 

 also appears to consist of a serpentinized olivine (poor in iron) and a few grains 

 of another mineral, probably once an enstatite, but now replaced by minute 

 antigorite (cf. the specimen from Val Antigorio) which sometimes exhibits an 

 approach to thorn-structure. 



2 This was collected (because of its curious look) so long ago as 1800. 



