414 Professor Bonney — On Limhirgite from Sasbach. 



and of an interstitial material, which sometimes is a brown glass, 

 sometimes a clear substance, more or less crowded with brown 

 granules. The latter not unfrequently acts on polarized light, and 

 in its clearer parts the outlines of a prismatic mineral, apparently 

 a felspar, may be detected. 



(2) Base of the middle mass, right-hand side. The hand specimen 

 exhibits many crystals of black augite about the same size as in the 

 first specimen, and small light-rust-brown spots, indicating partly 

 decomposed olivine, in a chocolate-brown compact matrix. Vesicles 

 are far from numerous, generally not larger than a mustard-seed, 

 and usually filled with secondary white minerals. As the larger 

 minerals — augite, olivine, and iron oxide — as well as the secondary 

 minerals, zeolites and carbonates, in the vesicles, have been so fully 

 described by Eosenbusch in his classic memoir on this rock,^ I shall 

 content myself with referring the reader to its pages, for they are 

 practically identical. The olivines (hyalosiderite), I may remark, 

 are frequently, though not universally, idiomorphic, and the augites 

 generally show a slight pleochroism. This is more marked in 

 longitudinal sections, giving a distinctly yellowish tint with vibrations 

 parallel to the vertical axis, and puce-brown with those perpendicular 

 to it. As in the normal limburgite, the larger minerals, augite, 

 olivine, and iron oxide, are rather thickly scattered in a groundmass 

 composed of felted minute prisms of puce-brown augite, with specks 

 of opacite, flakelets of ferrite, and some colourless belonites,^ and 

 a clear interstitial material, which in parts is doubly refracting, but 

 mostly behaves as a glass. This sometimes (though less frequently) 

 is of a rusty-brown colour, and recalls the base of the typical 

 limburgite. These augite prisms do not exceed -005" in length, 

 and are commonly four or five times longer than broad. The ferrite 

 flakelets act on polarized light, as do some little prisms of the same 

 colour, but I suspect this material to be little more than a staining. 

 The groundmass, I may add, is not unlike one figured by Boricky.^ 



(3) " From the left-hand side of the middle mass of limburgite," 

 and (4) "From the central part of the pit, a few feet above the floor." 

 Both these specimens hardly differ megascopically from No. 2, 

 except perhaps in being a shade less vesicular ; but this is not ti'ue 

 of their groundmass, which, however, is so similar in both, that one 

 description may serve. No. 3 contains numerous transparent lath- 

 shaped microliths, up to about -015" long, though in one case double 

 of this, and the clear material between these and other microliths 

 (augite, etc.) is doubly refracting, affording low polarization tints, 

 and resembling an indefinitely crystalline mass of felspar. The 

 microliths show the characteristic twinning of plagioclase, and 

 measurements of extinction angles incline me to refer them to 

 labradorite. The small prisms of augite are much less numerous 

 than in No. 2, but generally a little larger. The opacite and ferrite 

 are more or less inclined to cluster in rod-like patterns, and the 



1 Neues Jahrbucli, 1872, p. 33. 



2 I defer the description of these. 



3 *' Petr. Stud, an den Gesteinen Bohmens," pi. ii, fig. 8, and pi. iii, fig. 3. 



