721 
No. 170. Atheeton’s Ceeek, Heebeeton (Queensland). 
11. L. Jack’s Collection. 
Colour, greyish-klack. Very compact. 
Section . — May be described in the same language as No. 167, except that the 
minute felspar inicroliths are wanting, and the ground-mass is richer in augite granules. 
No. 171. Axheeton’s Ceeek, Heebeeton (Queensland). 
R. L. .lack’s Collection. Sp. Gr. 2‘733. 
Colour, purplish-grey. Small vesicles. 
Section . — The ground-mass is more glassy than in the preceding sam^^le. No. 170, 
and the augite is micrograuulitic, with a little magnetite in the ground-mass. The 
porphyritic augite is precisely similar in every respect to the last. The angle of 
extinction on the clinopinakoid subtends an angle of 24° with the edge of the crystal. 
The felspar inicroliths are long (about '92 inch), and seldom show more than 
two stripes. They gracefully sweep past the obstructing augites, giving a fairly well- 
marked fluxion-structure. It is by far the most interesting of the basalt collection, and 
the section is peculiarly thin. 
No. 251. Mitee Eock (New Guinea). 
Sir W. Macgregor’s Collection. 
Colour . — A dark greenish-black rock with yellow specks. 
Section. — Ground-mass pleutiful, consisting of a glass with innumerable felspar 
microlites and sharp grains of magnetite. The felspars do not exceed '001 inch in 
length, and the magnetite grains, which are wonderfully equal in size, measure '0002 
inch in diameter. Vine black dusty matter makes the glass obscure, but under the 
J-inch objective the constitution is resolved as given above. The porphyritic minerals 
are plagioelase and augite, both very fresh, particularly the felspars. Sanidine in Baveno 
twins with perfect zonal structure ; also in Carlsbad twins. The best example of the 
plagioclases several times twinned show angles of 26° and 24° 30' between the respective 
axes of elasticity and the traces of the twinning plane flf, so that the section must be 
nearly normal to that plane. It is not certain whether this section cuts the basal 
pinakoid or the clinopinakoid, but, whichever it may be, the formula of the mixture 
cannot be less than Al An.,* according to Eosenbusch’s table quoted in the granite 
series. Zonal structure occurs in the plagioclases. 
The augite is in large crystals, averaging '06 inch, showing marked cleavage. 
The angle between cleavage and an axis of elasticity is 28° 30'. The augites are but 
little altered. In some cases serpentiuization seems to have started. The inclusions 
are glassy and gaseous. No moving bubbles. 
No. 214. Lolwoeth Eun, feom the Eoot oe the Geanite Eange, Homestead, 
Cape Eivee (Queensland). 
W. 11. Eands’ Collection. 
A black, very fine-grained, compact rock. Carries no glass or pasty matter in 
the ground-mass ; might be a dolerite. The augite is micrograuulitic. The felspars 
are much striated. Compared with a section in a collection sold by E. Euess, of Berlin, 
* Where Ab represents albite and An anorthite. Vide Note on Roaenbusoh’s Felspar Formulse at 
end of Chapter. 
2x 
