﻿Vol. 6 1.] MICROSCOPIC STRUCTURE OF SERPENTINE. 703 



larger, but there are no differences of any importance. A slice 

 from the more massive serpentine only differs in not having the 

 granular iron-oxide so much ' trailed out,' and in containing a 

 number of minute granules, giving faiiiy-bright polarization-tints, 

 which possibly represent residual augite. 



The hillside then slightly recedes for from 200 to 300 yards, and 

 a path across it (leading up to the old castle) passes some serpen- 

 tine, a craglet of which exhibits crushed zones and a bluish 

 weathering. Another outcrop is obviously much crushed, but this 

 may not be in situ. Micaceous gneiss and schist also crop out on 

 the slopes, the castle standing on a knoll of stronger gneiss. 

 Miss Raisin made two other traverses across the serpentine, one 

 about the level of the castle, and one higher up the slope. On 

 the former she found the serpentine in bosses, near some small 

 cottages, much crushed and including a crushed talc-schist; and 

 on the upper she crossed an interesting vein about 3| feet long 

 and 6 inches wide — showing, like the surrounding serpentine, much 

 crumpling. 



The ' crushed flaky mottled rock, by the path to the castle,' 

 exhibits a rather crumpled foliated structure, and consists of the 

 following: — a colourless mica-like mineral; black iron-oxide in 

 more or less irregular patches ; and a fairly-large amount of 

 slightly -greyish or brownish granules, sometimes formiug thin 

 streaks. The flakes of the first are commonly about "015 inch 

 long, but occasionally almost double this. The polarization-tints 

 belong to the first order, and rise to yellow or brownish orange, but- 

 smaller flakes of the bluish-white variety are associated with it ; 

 though these are generally the smaller, we doubt whether the 

 difference is due to size alone. The slice also contains, though very 

 locally, a third variety, the tints of which never rise above a very 

 dull dark blue. The granular mineral is apparently residual 

 augite, the crystals of which have been crushed almost to powder. 



The talc-schist collected on the lower traverse proves, on micro- 

 scopic examination, to be a matted mass of that mineral, generally 

 resembling those described from the Gorner Grat 1 and Anglesey, 2 

 but it contains a rather large amount of a carbonate (?magnesite) 

 often with flecks of limonite deposited in its cleavages. The 

 crushed serpentine taken on the higher traverse shows the very 

 faintest trace of pleochroism (straw-coloured to pale dull green), and 

 consists of (a) the usual mica-like mineral, occasionally very 

 minute : sometimes showing ' thorn-structure ' and sometimes a 

 streaky 'foliation, indicative of crushing, in which the polarization- 

 tints become slightly higher than usual; (b) tho usual granules and 

 grains of iron-oxide ; and (c) a fair number- of granules or small 

 fragments of crystals, which resemblo residual augite, although their 

 extinction-angles, so far as they can be measured, agree better with 

 hornblende. The slice cut from the vein affords marked indications 



1 Geol. Mag. 1890, pp. 538, 510. 



2 Quart. Journ. Geol. Soc. vol. xxxvii (1881) p. 44, 



