7i4 
Ifo. 108 . Neli, Isee (New G-uiis’ea). 
Sir W. MacgTegor’s Collection. Sp. Gr. 2 407. 
Section . — A greyish glass filled with somewhat large felspar niicrolites, w^hich 
mark the fluxion-strueture, as in Plate t!l, and Plate 02, fig. 1. But even if the 
niicrolites were wanting the fluxion would still be well marked by the du.sty matter with 
which the glass is charged. The felspars are vety clear, almost limpid, and generally 
of a tabular habit ; though .some are prismatic, like the felspar, abutting on the olivine 
crystal in the three ligui'es on Plates 01 and 62. A felspar is shown thereon close to 
the margin, which is slightly inclined to the jtlane of the section. It is one of the 
tabular crystals, which, hading away from the olivine, has passed through the other 
side, where it has been ground off with the slice. Sanidine, twinned on the Carlsbad 
type, is pretty common, and exquisitely limpid. An olivine crystal is represented in 
each drawing, abutting on a felspar, and the structure of the glassy base, shows 
fluxion, as marked both by the inicrolites and the dusty matter. All three are magnified 
forty-two diameters — (1) polarized between crossed nicols, (2) with polarizer only, and 
(3) between parallel nicols respectively. 
The roughness of the olivine is shown in Plate 61, fig. 1. The black crystals 
on the margin and in the interior of the olivine are either magnetite or titanic iron, 
more probably the latter. Under the j-inch objective the microliths are peculiarly 
numerous. They can be divided into two classes, — first, a large form of microlite, as a 
rule measuring about '0005 x •004 inch, which are alwaj^s stepped like the drawing gix'en 
ill Kosenbusch* ; and, second, hair-like microliths, which, however, are not triohites, 
being transparent. The brownish-grey w'ave flowing over the felspar, shown in the 
drawings, is very rich in these minute microliths. The feathered edge of glassy base on 
the other felspar, just peeping out at the surface, on the right-hand side of Plate 61, 
fig. 2 (also showing in Plate 62, fig 1), becomes very useful, as it enables us to get 
a clear view of these small bodies without the image getting blurred by a background 
composed of the same bodies, in different azimuths. In one of the clearest and most 
limpid of the sanidines is a very curious growth of what I take to be a glass inclusion. 
The growth starts from a point on the margin of the crystal, and branches out not 
unlike a fern, but that the divergent branchlets are clubbed at the end, and are a pale 
hyacinth colour. 
TEAOHYTE. 
No. 24. GnAnsTONE (Queenslaitd). 
B. L. Jack’s Collection, Sanidine Trachytes. Sp. Gr. 2'79. 
Colour, dirty whitish-red; with somewhat large crystals of sanidine. Very 
porous, with a few small cavities not unlike the smaller holes in a sponge. 
Section. — Ground-mass plagioclase, showing fluxion-strueture ; quartz in very 
small allotriomorphic grains; sanidine, clear. One sanidine crystal is well marked 
with curved markings as drawn by Butley in the “ Study of Bocks” (p. 96, hi. edition) 
and sometimes tabular, being parallel to M ; at other times the sanidines are twinned 
on the Carlsbad type. By reflected light one sees a very thorough sprinkling of the 
whole slice with brownish-red ferritic matter, and a whitish-y’ellow substance, both 
amorphous. Only the sanidines escape the peppering. 
The slice being somewhat thick it is difficult to make out the glass that ought to 
be present. The only glass observable is that lining the interior of cavities. 
Physiography of the Rock-making Minerals. 
