﻿706 PROF. T. G. BONNEY AND MISS C. RAISIN ON THE [Nov. I905, 



schists of the Gorner Grat) we find a little of a flaky greener 

 mineral, faintly pleochroic in that colour, and producing but small 

 effect on polarized light. From the north of the castle comes a 

 specimen, not much crushed, which has been an olivine-enstatite 

 rock x ; the serpentine replacing the former mineral produces more 

 effect on polarized light in the ' strings ' than in the meshes, but it 

 approaches once or twice the antigorite-' habit ' : that replacing the 

 enstatite needs no special description. Of four specimens from a 

 crag and blocks near a waterfall : one, resembling the rock from 

 near the shrine, but with brighter polarization-tints, is a variety of 

 talc-schist ; another is rather banded ; flakes producing dull white 

 polarization-tints 2 dominating in one part, a very minute mineral — 

 perhaps the same — in another, and in a third, a mineral affording 

 rather bright polarization-tints, with apparently-straight extinction 

 — perhaps a peculiar form of antigorite. The other specimens, which 

 contain normal antigorite, do not call for any special remark — 

 except that one is about as much crushed as some of the slaty 

 serpentine described in the next section. 



Thus the serpentines of the Brenner district prove (a) the ex- 

 istence of antigorite (including the variety with slightly-higher 

 polarization-tints) in close association with augite, but without any 

 relation to its prismatic cleavages ; (b) that pleochroism is not an 

 essential property of antigorite, but probably depends on the acci- 

 dental presence of some colouring-matter ; and (c) that we have 

 failed to find any mineral resembling staurolite. 



X. Other Alpine Serpentines. 



The Alpine serpentines, as one of us has more than once pointed 

 out, can be arranged in two fairly-distinct groups, namely, altered 

 olivine-enstatite rocks, with or without some augite, and olivine- 

 augite rocks often rich in the latter mineral. He has found the 

 former in situ on the Col de Cristillan, the Col de Sestrieres, 

 the Mont Genevre, in the Yal d'Anniviers, and once or twice in the 

 Central Pennines, near Davos, at more than one place between 

 Tiefenkastell and the Julier Pass, and by the Silser See : 3 the 



1 This difference in the parent-rock is noticed by Dr. Hussak, and in Zirkel's 

 • Lehrbuch der Petrographie ' 2nd ed. vol. iii (1894) p. 395. We have, however, 

 noted some residual augite in a second (less crushed) specimen from near the 

 shrine. It also has contained olivine and perhaps enstatite. 



2 This also, as in the specimen described above, is suggestive of a chlorite ; 

 but, on the whole, I incline to regard it as an abnormal antigorite. A speci- 

 men in Miss Eaisin's collection from Cerig Moelion, Anglesey, with much of 

 this mineral, some altered enstatite, and residual cliallage confirms this view. 

 [T. G-. B.] 



3 But I found, south of the Bernina, at the junction of the glens from the 

 Muretto and Canciano passes, a serpentine consisting largely of antigorite 

 (polarization-tints up to yellow) with a fair amount of residual augite (some 

 stained sienna-brown) and a little of a chlorite; the serpentine also above 

 Lanzada (with ' asbestos '), on the west side of the latter pass, contains residual 

 augite and antigorite in rather foliated flakes, sometimes "04 inch long, the 

 polarization-tints ranging up to the pale yellow of the first order. [T. Gr. B.] 



