498 Prof. Bonney and Miss Raisin — Rocks from. Kimherlerj. 



to that described above, but almost certainly of secondary origin. 

 With mica, perhaps, may be included some rather regular hexagonal 

 thin plates, of an apparently colourless mineral, which seem to 

 project into interspaces; (c) chlorite (?) ; {d) needles, often radially 

 tufted, clear and colourless, with low polarization tints and probably 

 straight extinction ; (e) a carbonate, seemingly varying from calcite 

 to dolomite, filling up interspaces; and probably (/) a little opal. 



As to the rock fiagments, our specimen of the breccia has not 

 aflbrded either granite or pegmatite, rocks which were detected by 

 Prof. Daubree. Those present, as described above, have a hardness 

 generally a little less than 4, but one large fragment, paler in 

 colour than most of them, is about 2-5. Under the microscope the 

 outermost zone is usually thin, sometimes consisting rather largely 

 of an aggregate of minute chlorite, followed by a second and broader 

 zone containing films of brown mica^ with ill-defined outlines ; the 

 third zone is often rich in minute perofskite. In other cases the ex- 

 ternal zone is richer in perofskite, and within this comes a greenish 

 zone, which may be followed by another perofskite band, sometimes 

 broad. The inner part of the fragments is rather "patchy" in 

 structure, consisting, in some cases, very largelj^of a clear colourless 

 isotropic material (? a hydrous glass). In this, scattered in rather 

 varying quantities, are (a) clusters of perofskite ; (fc) films of brown 

 mica (biotite) as above, in one or two cases sprouting inwards from 

 the inner zone ; (c) minute acicular prisms, giving low polarization 

 tints and straight extinction, often forming tufted or radiating groups 

 (occasionally almost spherulitic), which in a few cases seemingly 

 are growing from the ends of the brown mica; {d) rude attempts at 

 skeleton crystals, probably magnetite ; (e) a carbonate (as in the 

 matrix). 



Three fragments differ somewhat from the rest. One includes 

 serpentinized olivine surrounded by a material, which exhibits a 

 structure suggestive of a flowing. Another consists of grains and 

 granules of serpentinized olivine, with thin flakes of brown mica 

 and pseudobrookite or chromite. The third with transmitted light 

 looks almost pellucid, but with crossed nicols exhibits an aggregate 

 structure, such as may be seen in a serpentine, though on a very 

 minute scale, the constituents being grouped in lighter and darker 

 parts, as may be sometimes observed in a scoriaceous rock. One 

 corner, however, exhibits a spherulitic structure, which also makes 

 its appearance here and there in other, commonly the outer, parts of 

 the fragment. 



The general aspect of these fragments (except for the zones) 

 recalls certain varieties of much decomposed serpentine, and to this 

 rock, though we have never seen any quite identical, we venture to 

 refer it, believing that it is the result of the alteration of either 

 a glassy or a very minutely crystalline peridotite. The zonal 

 banding may be original, as it recalls that exhibited by fragments 

 in some diabase tuffs from Porthdiulleyn,^ where it is an original 



^ The biotite is variable in amount, and occasional!)' is wanting. 

 "^ Cf. C. A. Raisin on Variolite .... of the Lleru : Quart. Joum. Geol. 

 Soc, vol xlix, 1893, p. 151. 



