﻿Vol. 64.] AN^D ANTIGOEITE-SERPENTINES. 165 



olivine/ In a few the matted antigorite is traversed by tiny 

 strings of opacite resembling those in a serpentine formed from that 

 mineral, or it occupies small spaces in one of the larger grains of 

 pyroxene, suggestive of poecilitic olivine ; but that antigorite can 

 be produced from olivine seems to be certain. Dr. F. Becke, in his 

 valuable paper on ' Olivinfels & Antigorite-Serpentine ' from the 

 Stubachthal,'- distinctly states that the unaltered rock consists of 

 olivine and picotite, sometimes with a diopside. It shows signs of 

 a cataclastic structure, and flakes of antigorite can be seen in the 

 cracks of the grains of olivine, separating them into granules, but 

 not forming so characteristic a meshwork as in the ordinary process 

 of serpentinization, while in other parts of the mass the change to 

 an antigorite-serpentine is complete. Dr. H. Preiswerk ^ also, in his 

 concise and interesting account of the serpentine at the upper part 

 of the Geisspfad Pass, says that the mass in its central portion is 

 a dunite, though it contains dial] age towards the periphery, where 

 it occasionally becomes almost a diallagite. Antigorite is produced 

 from both its minerals, but seems to come more directly from the 

 pyroxenic constituent, and a little actinolite is a usual alteration- 

 product.'^ Again, Dr. J. M. Bell in his reply, dated December 7th, 

 1907, to an enquiry about the specimens of antigorite - rock, 

 forwarded to me from New Zealand, says : 



*I feel confident that the parent rock was mainly olivine, with perhaps a 

 little pyroxene, either orthoiliombic or monoelinic. One gets apparently the 

 transition of this rock into dunite.' 



In No. 3 of the Bulletin (' The Geology of the Parapura Subdivision, 

 Karamea, Nelson '), for which I am also indebted to him, serpentines 

 and talc-schists (sills and perhaps dykes) are described (Ch. ix), 

 which break through highly matamorphic strata and may possibly 

 be of Haupiri ('? Devonian) age. The former consist chiefly of 

 antigorite, with minor quantities of talc, chromite, etc, ; the latter, 

 no doubt a further stage of alteration, due partly to pressure, pass 



^ Last autumn, a friend suggested to me that some clear sienna-brown grains, 

 in a slice from a specimen obtained on an old moraine Tiear the Findelen 

 Glacier, were titanolivine. As his experience is large and that mineral has 

 been obtained in this district, I have again examined not only that slice, but 

 also the others with residual pyroxene. The form of the grains, however, is 

 more suggestive of augite than of olivine ; a rudely shaped prism may be tinted 

 at one end, clear at the other ; the pleochroism seems hardly strong enough 

 for titanolivine, and the extinction in both coloured and uncoloured grains is 

 oblique and like that of augite. Hence I think the former only a result of 

 staining (see our paper of 1905, p. 706). 



^ Tschermak's Min. Petr. Mitth. n. s. vol. xiv (1894-95) p. 271. 



3 Eclog. Geol. Helvct. vol. vii (1901-1902) p. 123. 



"* R. von Drasche, Tschermak's Mineral. Mitth. p. 1, in Jahrb. K. K. Greol. 

 Eeichsanst. vol. xxi (1871), describes the formation of antigorite (without, 

 however, using the name) from an olivine-rock. The Cogue serpentines (see 

 Quart. Journ. Geol. Soc. vol. lix, 1903, pp. 58-60) on the whole favour the 

 formation uf antigorite from olivine. 



