﻿Vol. 6 1.] MICKOSCOPIC STRUCTURE OF SERPENTINE. 707 



other is especially common in the Pennine Alps between the Col 

 du Collon and the Sirnplon Pass, and occurs also near Cogne. 

 Alpine serpentines are sometimes so much affected by pressure 

 as to become perfectly slaty. Such he has found near the Col de 

 Vallante (Viso), at Verrex in the Val d'Aosta, on the Gorner Grat 

 and at the base of the Itiffelhorn, where flakes can be obtained no 

 thicker than a postcard. 



For the microscopic structure of the first group we may refer 

 to descriptions already published. 1 Except for occasional effects 

 of pressure, they do not differ from serpentines of similar com- 

 position from Scotland, Cornwall, and the Apennines. For the 

 second group also, if that so abundant about the head-waters of 

 the Visp be accepted as an example, we may refer, in most cases, to 

 what is already in print. This serpentine is usually harder to 

 scratch or to break, 2 a little more granular to the eye, and rougher 

 to the touch than that obtained at the Lizard, and very rarely, if ever, 

 shows any trace of enstatite. Even when most compact, it breaks 

 with less ease and with a less curd-like fracture than the other 

 serpentine. Put even then the microscope generally reveals some 

 minute residual grains of augite, while the more granular kinds 

 are rich in that mineral. Many of them are megascopically 

 identical with specimens brought by Miss llaisin from Sprechenstein. 



We will first briefly notice five specimens, hitherto undescribed, 

 from the upper part of the Saasthal. The first, from the smallest 

 of the three well-known great boulders on the valley-floor above 

 the Mattmark Hotel, must occur in situ, either on the eastern face 

 of the Strahlhorn or in a spur running from it to the north-east. 

 The microscope shows the rock to have suffered from pressure, to 

 contain more than the usual amount of magnetite (with a little 

 pyrite), much augite, both residual and in larger, dusty, brownish 

 grains frequently showing diallagc- cleavage — perhaps making up 

 altogether one-fifth of the slice, — while the rest consists of the two 

 varieties of the mica-like mineral (antigorite), as mentioned above, 

 the one with bright tints, generally, but not always, the larger, 

 perhaps a little less definitely cleaved, and certainly sometimes 

 giving a slightly-oblique extinction up to about 10° or 12°. In 



1 Quart. Journ. Gcol. Sue. vol. xlv (1889) p. 81 & Geol. Mag. 1880, p. 538. 



2 lis hardness is generally higher in the scale than that of the other variety, 

 sometimes nearly a degree. As Miss llaisin observed in the Brenner district 

 (p. 701) the more schistose specimens are less hard and rough than the others, 

 [Since this paper was read I have again visited the Saasthal, and examined 

 many boulders on the moraine of the Fee Glacier and in the valley above Almagell 

 (that is, representing another set of outcrops). The waterworn blocks commonly 

 have a characteristic smooth, rather mottled surface (pale and dark green) ; they 

 are much tougher than the ordinary serpentines, and feel so much harder and 

 (commonly) 'harsher' in the hand, that I believe I could distinguish them blind- 

 fold. I failed to find any specimen of the ordinary (oli vine-enst atite) serpentine. 

 I may say that the work of the past two years has proved to me that augite has 

 been, at any rate sometimes, a still more abundant constituent in this second 

 group than I formerly supposed. — T. Gr. B.] 



