﻿62 Rev. T. G. Bonney — The LherzoUte of the Ariege. 



is represented to some extent, as in the last, in the paste. In this 

 (in the last two cases) one can readily distinguish bright green 

 fragments of diopside and rather numerous black grains of picotite, 

 apparently imbedded separately. 



This mass of Lherzolite is the largest of the seven exposures in 

 the district, and according to Prof. Zii-kel is about 1300 yards in 

 greatest length. Three other masses lie near it along the line of 

 the little glen of the Sue. The rest are near its junction with the 

 Oriege, one being on the opposite bank near the village of Sem. 

 All are in the Liassic rocks, and, except the last, are very near their 

 junction with the granite, which even here is at no great distance. 

 It is also more coarsely granular than the rock at the Etang, and the 

 breccia is wanting. Lherzolite also occurs near Portet d'Aspet, in 

 the upper Val longue (Castillon) , and on the south side of the Col de 

 Lurde, in the neighbourhood of Eaux Bonnes. The principal rock 

 here is a limestone with ophite, i.e. greenstone, near it. I have not 

 seen any of these. 



The rather compact condition of the rock, and the fact that the 

 olivine is in soine specimens rather green, and the diopside a little dull 

 in colour, while the enstatite does not always exhibit its characteristic 

 structure, makes it often very hard to distinguish the component 

 minerals of the specimens from the Etang de Lherz. They are better 

 seen, however, on a polished surface, and can be separated, as 

 Zirkel suggests, by treating the pounded rock, first with hydro- 

 chloric acid, and then boiling it with caustic potass. In my 

 Pisani specimen from Sem, the minerals are much more easily dis- 

 tinguished, as is the case also, according to Zirkel, in his specimens from 

 this locality. The composition of the Pyrenean Lherzolite is according 

 to an old analysis (Zirkel, p. 140) : — SiO2=45-0, Al2O3=l-0, CaO= 

 19-5, MgO=16-0, FeO=12-0, CrO=0-5, with a trace of MnO 

 and loss=6-0. Lasaulx gives the analysis of a Lherzolite from 

 Norway (Elem. der Petrograph. p. 338) :— 8102=3742, Al203= 

 0-10, MgO=48-22, FeO=8-88, MnO=0-17, NiO=0-23, H202=-71. 



The rock varies slightly in different parts around the Etang, 

 both in grain and in preservation. I collected s^iecimens chiefly 

 from near the southern end, and about half-way down the west 

 side ; the most serpentinous specimens coming from the former. 

 Mr. S. Allport, to whom I gave a duplicate from Sem, kindly cut 

 me a beautiful slide from it, and I have had slides (six in all) 

 cut from three varieties collected by myself at the Etang. I will 

 refer to them as No. I. (from Sem [Pisani]), No. II. (specimen from 

 the west side), No. III. (specimen from the south end), No. IV. 

 (specimen showing a partial passage into serpentine). This speci- 

 men was cut close to a joint face where the change was greatest. 



Microscopic Sh'ucture. — In all cases the rock is normally com- 

 p)0sed of olivine, enstatite, diopside, and picotite, with occasional 

 minute specks and mlcrollthlc aggregates of an opaque black mineral, 

 probably magnetite. Microliths of other minerals are rare. The 

 first three minerals all occur in variable shaped grains; those of 

 the olivine roundish ; the diopside occasionally showing a slight 



