﻿60 Rev. T. G. Bonney — The Lherzolite of the Ariege. 



above the bed of the former. On the opposite side of this rises a bare 

 craggy limestone hill, capping the Lherzolite which forms its base. 



The Lherzolite is tough and difficult to break, traversed by many 

 minute, rather irregular, divisional planes, with occasionally a slight 

 tendency to a platy structure. Hence it is not easy to obtain good 

 specimens. The surface of a specimen from the heart of the rock 

 is rough, rather uneven and granular, at the first glance tolerably 

 uniform in colour and apparent composition, of a dark greenish - 

 grey or olive-green colour. A closer examination shows specks of 

 brighter green, generally of two colours, one (the more invariable) 

 an emerald green, the other a waxy-looking duller green ; also specks 

 of a resinous pale-brown mineral, sometimes with a platy or fibrous 

 aspect and a dullish lustre ranging from silvery to brassy. Minute 

 grains of an irregularly disseminated black mineral, with a vitreous 

 lustre, are also just visible; and there is another of transparent glassy 

 aspect. The last is only broken olivine, to which the predominant 

 dull-coloured mineral belongs ; the emerald green is the diopside : 

 the resinous mineral enstatite; and the black is picotite. The duller 

 green tint is serpentine. The separate minerals are more easily 

 detected in a coarser specimen, which I purchased from Pisani in 

 Paris in 1875, who obtained it from Sem, the easternmost locality 

 along this line of outbursts in the Department of Ariege. 



The rock at the Etang de Lherz varies a little in texture, some, 

 especially, as it appeared to me, that towards the outside, being more 

 compact than the rest. When the rock is slightly decomposed the 

 dull green tint becomes more marked, and the compact varieties 

 begin to resemble serpentine. The exterior weathers from a bright 

 yellowish to a dark rusty-brown tint, with a rough surface. On this 

 the projecting pale amber-yellow grains of enstatite, and the bright 

 green grains of diopside, with the black picotite, may be readily 

 distinguished. Occasionally also a sort of linear structure is developed 

 on the surface in weathering ; such as I have observed in some of 

 the Lizard serpentine ; like this, it has some connexion with an 

 internal parallelism, but the exact nature of it is not yet quite clear 

 to me, though I think it will prove to be connected with a fluidal 

 structure. The brown weathered surface generally extends inwards 

 for about •! to -2 inch ; and the change from it to the green rock is 

 pretty sudden, a thin pale band usually intervening, in which the 

 enstatite, diopside and picotite are well distinguished. The rock is 

 traversed by numerous irregular joints, breaking it up into rude 

 polygonal blocks ; but now and then the outside of an old weathered 

 surface shows a more regular prismatic structure ; occasionally also 

 there is a slight parallelism in its fissures. The more minute joints 

 are lined with a thin film of limonite or of a serpentinous mineral, 

 apparently a green steatite, — often in the latter case so thin as to be 

 a mere glaze. Slickensides are not rare on the joint faces. The 

 general aspect of the weathered rock, the peculiar roughened surface 

 with its irregular fissures, the jointings and contours of the fallen 

 blocks, in shape like masses of broken curd, strongly reminded me 

 of the Lizard serpentine in Cornwall, with which I am very familiar. 



