703 
Felspars frequent and fairly fresh, consisting of orthoclase, microcline, and 
plagioelase. The first is the least'fresh, and often there is an intergrowth of the first 
two mentioned. The microcline is exquisitely lined, markings under the i-inch being 
finer than the finest lines in a good steel engraving. The simultaneous e.xtinetion of 
the two sets of cross lines is marked ; one set of cross lines is less perfect than the 
other, being slightly spindle-shaped or wedged. The angle between the two sets of 
lines varied between 91° 30' and 93°, but it is not easy to see when the cross web exactly 
coincides with the less regular cross lines of the felspar, so that the angle in no case is 
quite accurately measured. In the plagioclases the angle between the traces of the 
twinning planes and an axis of elasticity is between 7° and 10°. In one case the 
angles of extinction on either side of the twinning planes were 8° 10' and 7° 30' — angles 
so nearly equal that it will be safe to assume that the section of the crystal is cut parallel 
to the zone at right angles to M. The nearest angle to the mean of these given in 
Eosenbuseh* * * § is 7° 35', which would give a formula to these felspars of Ah® and Au'‘.t 
Quartz rich in inclusions and microlites. The inclusions are sometimes fluid and 
dihexahodral, with moving bubbles. The microlites are an interesting feature in the 
rock, as they closely resemble those in the quartzes of granite found at Summit 
Springs, TTovallah Eange, North America, described and drawn by Zirkel ; but he 
describes them as being black, whereas the microlites in the quartzes of my section are 
milk-white by reflected light, strongly resembling the raphides found in Typha 
angusHfolia, Linn.,J except that the microlites much exceed the raphides in length. 
The quartzes do not always polarize uniformly, and may be described, according 
to Professor Hutton’s nomenclature of rock textures, as granulitie.§ 
The Mica is a dark-brown biotite, and very sparsely distributed. 
No. 14. CooKxowir (Qtteknslani)). 
F. Bauer’s Collection. Sp. Gr. 2 '6437.11 
Colour grey. Granular, allotriomorphic. Felspars large, commonly |^-inch and 
sometimes |^-inch long, idiomorphic, cleavage well-marked when held in light falling 
on it obliquely. Sparsely scattered allotriomorphic quartz. Little hornblende. Biotite 
and tourmaline in minute black shining grains and prisms. 
Quartz rich in inclusions, varying considerably in size, a few just visible under 
the 1-inch objective ; some fluid, with moving bubbles ; others with fixed gas pores, also 
glass inclusi ons. They are all spread out in planes traversing the crystal and crossing each 
other at low angles. The more persistent are rudely parallel to an axis of' elasticity, 
possibly the principal axis. The micrometer screw shows how they “hade” in all 
directions. What I take to be the glass-inclusions are very irregular in outline, being 
pear-shaped, globular, and quite irregular, resembling the smear left by an oily finger 
on perfectly polished glass or the magnified image of a finger-mark on a glass-slip such 
as is used for mounting microscopic objects. 
Felspars much decomposed, showing the clear, straight lines described in the 
Croydon granite. No. 26 (probably orthoclase). 
* “ Microscopical Physiogranliy,” p. 300. 
t Where Ab represents albite, and An anorthite. Vide note at end of Chapter. 
X A bulrush infesting tailings-dams at Charters Towers. See “ Synopsis of the Queensland Plora, by 
P. M. Bailey, p. 571. Brisbane : by Authority : 1883. ^ -d i 
§ Prof. Hutton’s Catalogue of Kock Textures, as given in his Paper, on The Eruptive Rooks of Rew 
Zealand.” (Proo. R. Soo. N.S. Wales, 1890, xxiii., p. 107.) 
II In determining these Sp. Grs., as large a piece of rook as could be procured has always formed the 
material for experiments. The piece used in this determination weighed p,lbJ grams, which warrants 
carrying the calculation to the 4th decimal place. This rule has been observed throughout. 
