711 
felspars . — About tliree-fourtlis of the section is made up of the lath-shaped 
felspars, which are opaque, even on the edges of the section which is always the thinnest 
part, being feather- edged, One much altered felspar shows the fine .striie in the centre, 
but it becomes lost on the margins, whore the kaolinization has eSaeed it as a felspar. 
Another felspar A inch long, is very clear, and for a portion of its length is nearly 
•Olo inch broad, and shows the traces of twinning plane J/ very clcaidy. Quartz, crossed 
by very pale, slender needles, probably hornblende, inclusions unimportant and sparse. 
Hornblende well marked when cut parallel to o P, showing cleavages crossing at the 
angle of about 125°. Magnetite abounds. Thelargerparticles, however, are found more 
often in the neighbourhood of the hornblende, associated with apatite. Biotite showing 
marked absorption for the rays vibrating parallel to cleavage. When cut parallel to 
the base they are difficult to identify, owing to their granular state. A little pyrites in 
minute cubes in the powder when panned off. 
Xo. 74. Mackat (Queenslasd). 
A. G-. Maitland’s Collection. Sp. Gr. 2'68. 
Colour, dark greyish-brown. Highly felspathic, hornblende, and very little 
quartz. 
Sectioii . — The bulk of this rock is make up of triclinic felspars, '07 to '1 inch in 
length. Originally, these felspars must luave been extremely beautiful — even now the 
striations are exquisitely regular when not marred by kaolinization. 
In one mass of twins there are ninety-three lamelhe, broken here and there by 
opaque secondary minerals, but the stripe, s pass “through” the shadow, as it were, and 
emerge clean-cut and bright. The angles of extinction, with reference to the twinning 
planes are, right 2°, left 9° 40', and in another, right 2° 50', left 8° 30'. Again, in another, 
whose colours, in maximum illumination between crossed nicols, are, for one set of 
lamellffi, pale-yellow ; for the other, white. The angles are, right, 2-4°, and left, 5°. 
Another gives right, 1° 10', and left, 7°. 
Orthoelase occurs in the usual Carlsbad twins, but not plentifully. All the 
felspars exhibit more or less unduloes extinction. 
The angles given above are taken from the central extinction as far as possible. 
In one or two cases the stripes have violet centres and blue ends, with the quartz plate 
and the analyser arranged for a violet field. Hornblende reedy (“ schilfige”) and 
absorption feeble, much epidotized. The crystals have been seriously mutilated in the 
pi'ocess of grinding, the centres of nearly all being ground away, leaving microliths of 
hornblende in a ragged state, arranged marginally around cavities originally occupied 
by the mineral. 
Magnetite and apatite, the former always and the latter occasionally, associated 
with the hornblende. The apatite, however, is small and infrequent. One or two 
hexagonal sections of apatite occur in the felspar.s. 
Quartz in allotriomorphic grains, playing an insignificant part in the constitution 
of the whole rock, pretty much of one size, '01 inch in diameter. The enclosures are 
normal but large, in some cases fluid, in other cases glassy, and in a few gaseous. A few 
translucent oxide of iron specks, only visible under the ;^-inch objective. 
No. 23. Boulbee Cbeek, Silent Gkove, near Mackat (Queensland). 
A. G. Maitland’s Collection. 
Colour, red. Granular, allotriomorphic, holocrystalline ; the contained minerals 
include what looks like pink orthoelase, quartz, and a little hornblende. No mica 
visible in hand specimen. 
