126 MEMOIRS OF THE QUEENSLAND MUSEUM. 
ALPHA TORBANITE. 
General and Macroscopic. 
Locality of sample chosen for study: Tommy Staines Gully, portion 4, 
parish of Avonmore, county of Drummond, approximately 35 miles S.S.E. of 
Alpha. Geological Horizon: ? Lower Bowen Series. Age: Lower Permian. 
In the hand specimen this is a fine-grained, compact, homogeneous rock 
of dark brownish-black colour. It has a dull silky lustre, and a sub-conchoidal 
fracture. It is tough and massive, only indistinct traces of bedding being 
visible. It is comparatively soft, and gives a yellowish-brown streak. The 
specific gravity is 1-09. It ignites readily and burns with a bright flame, 
producing a waxy, aromatic odour. 
From the above physical properties the hand specimen is identified as a 
medium-grade, dull melanocratic torbanite, adopting Dulhunty ’s (1943) 
classification. 
Microscopic. 
(Plate XII, figs. 1, 2.). 
Horizontal and vertical sections of this rock have shown that it exhibits 
a definite microscopic structure. It is made up of translucent algal material, 
consisting mainly of gelosite and retinosite bodies, separated by films of opaque 
matrix. Estimations made, using the eye-piece micrometer, of the percentages 
of gelosite and retinosite present have given an average of 66 per cent, gelosite 
and 4 per cent, retinosite. This places the rock on the borderline between a 
medium-grade and high-grade torbanite. 
In the vertical section the translucent bodies are elongated in shape, 
lying parallel to the bedding plane, and in most cases the collapsed central 
cavity of the algal colonies can clearly be seen. The ratio of length to thickness 
determined for a large number of these flattened bodies has been found to 
average about six to one. 
In the horizontal section the translucent bodies are roughly rounded in 
shape, closely packed, and separated by opaque material. They show considerable 
variation in size, ranging in diameter from about 0-1 to 0-75 mm. Many of 
them have a series of bulges, which represent simple algal colonies, round 
their margins, and the bodies in such cases have something of a botryoidal 
appearance. Unlike spores they do not possess hard and well-defined margins, 
but tend to fray out into the opaque groundmass. 
Apart from the variation in the size of the translucent bodies, the 
microscopic structure or fabric of the rock is uniform and it is essentially 
non-banded. 
Under ordinary transmitted light the gelosite, which is by far the most 
abundant maceral in the rock, is pale yellow in colour and almost transparent. 
It has a low relief with the refractive index very close to that of Canada balsam. 
