﻿Rev. T. O. Bonney — The Lherzolite of the Ariege. 59 



shale, apparently at a high dip, which the Carboniferous betls of the 

 neighbourhood are not, traversed by several dykes of mica tx'ap. 

 These dykes are quite unlike anything else in the country ; but 

 resemble similar dykes in the Kendal country, where they are never 

 known to pierce the Carboniferous beds, but are exclusively confined 

 to the Silurian rocks. The hardened shale traversed by these dykes 

 in Teesdale is not unlike Skiddaw slate, which also was once 

 similarly worked for slate pencils in Westmoreland ; but 1 cannot 

 assert, merely after a short visit on a stormy Sunday afternoon 

 in November, that the shale is not hardened Carboniferous shale, 

 hardened by the dykes : but the beds are as much like Skiddaw 

 slate as Carboniferous shale, perhaps more so ; and this similarity, 

 together with the apparent high inclination, and the Silurian 

 character of the dykes, when taken along with the breccia at 

 the base of Falcon Clints, leads one to ask the question at the 

 head of this notice. 



V. — The Lherzolite of Akiege. 



By the Eev. T. G. Bonnet, M.A., F.G.S.; 



Fellow and late Tutor of St. John's College, Cambridge. 



THE rock Lherzolite has been described bj'- Prof. Zirkel in his 

 valuable Beitrage zur Geologischen Kentniss der Pyrenaen 

 {ZeitscJirift der Deutsch. Geol. GeseL, vol. xix. p. 68), but is generally 

 passed over with the briefest mention or entirely omitted in English 

 works on Geology. Even in Cotta's " Kocks Classified and Described " 

 it is barely noticed, and the word is left out in the index. On this 

 account, and seeing that, so far as I am aware, no description of its 

 microscopio structure has yet been published, a notice, embodying 

 the results of Prof. Zirkel's paper, and of a brief visit of my own to 

 this not very accessible locality, may be useful to students. 



Lherzolite is a crystalline aggregate of the minerals olivine, en- 

 statite, and diopside, with some picotite, in texture varying from 

 finely to rather coarsely granular ; that from the locality visited by 

 myself being, on the whole, of the former character. It obtains its 

 name from the Etang de Lherz, a small tarn in the Eastern Pyrenees 

 (Dept. Ariege), above Aulus, in the valley of the Garbet, 38 kil. 

 from St. Girons, and near the Col d' Erce (or Port de Lherz), an 

 easy pass (5341') leading to Vicdessos in the valley of the Oriege. 

 The rock entirely surrounds the Etang, and is the largest of a linear 

 series of seven exposures in the vicinity of Vicdessos. 



The Etang de Lherz is a shallow tarn occupying apparently a true 

 rock-basin, the longer axis of which lies roughly N. and S. The 

 water escapes from the northern end by soaking through some peaty 

 ground. On the western side is a tiny island. The tarn is sur- 

 rounded by rounded masses (probably once ice-worn) and fallen 

 blocks of the Lherzolite, which also rises from the western shore in 

 a craggy hill. A furlong or less from the eastern shore limestone 

 shows through the grass and stretches away in that direction, forming 

 the general mass of the country. The tarn is not in the line of the 

 main valley of the Garbet, but in a sort of open upland glen, a little 



