60 
liev. T. G. Bonney — The Lherzolite of the Ariecje. 
above the bed of the former. On the opposite side of this rises a bare 
eraggy limestone Kill, capping the Lherzolite which forms its base. 
The Lherzolite is tough and difficult to break, traversed by many 
minute, rather irregulär, 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 granulär, 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 vitreons 
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 Ai-iege. 
The rock at the Etang de Lherz varies a little in texture, some, 
especially, as it uppeared to me, that towards the outside, being more 
compact than the rest. When the rock is sliglitly decomposed the 
dull green tint becomes more marked, and the compact varieties 
begin to resemble Serpentine. The exterior weathers fi'om a bright 
yellowish to a dark rusty-brown tint, with a rough surface. O 11 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 thinlc it will prove to be connected with a fluidal 
structure. The brown weathered surface generally extends inwards 
for about T to -2 inch ; and the change from it to the green rock is 
pretty sudden, a thin pale band usually iutervening, in which the 
enstatite, diopside and picotite are well distinguished. The rock is 
traversed by numerous irregulär joints, breaking it up into rüde 
polygonal blocks ; but now and then the outside of an old weathered 
surface shows a more regulär 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 irregulär 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 familiär. 
