THE PETROGRAPHY OF SOME QUEENSLAND OIL SHALES. 
125 
TECHNIQUE IN PREPARATION OF THIN SECTIONS. 
For the preparation of thin sections of the oil shales described below 
the normal procedure in rock sectioning was found to be unsatisfactory, and 
the following technique had to be developed. 
Slices which were cut parallel and at right angles to the bedding (for 
horizontal and vertical sections) were ground first with 100-hole London Emery, 
and then with Emery Flour in the ordinary manner. Owing to the soft nature 
of the oil shales, however, it was necessary to continue grinding in order to 
remove scratches with a very fine hone held in a sloping position and kept 
continually wet by playing a thin 
stream of water upon it. Finally, the 
surface was given a high polish with 
Goddard ’s plate powder, which is also 
an exceedingly fine abrasive. Then, to 
avoid harming the material by mount- 
ing directly in Canada balsam heated 
to a high temperature to drive off the 
volatiles, the Canada balsam was first 
cooked in the usual way, and allowed 
to cool. It was then very carefully 
reheated, and when just remelted the 
slab was mounted, rather more 
pressure than usual being applied to 
squeeze out air bubbles from the 
viscous balsam. In this way the oil 
shale was mounted without any 
damage being done to it. The same 
method was then followed again in 
grinding the mounted slab down to 
the required thinness. As this was of 
the order of 0-005 mm., considerable 
care had to be taken during the final 
grinding. It was also necessary to 
avoid a high temperature in attaching 
the cover-slip to the slide, but 
satisfactory results were obtained by heating at a very low temperature for a 
prolonged period. Finally, to avoid the possibility of future wrinkling of the 
very thin section, a fiat weight was placed on the cover-slip for several days. 
Text-figure 1. — Map showing geographical 
location of the Alpha, Carnarvon, The Narrows, 
and Strathpine deposits. 
PETROGRAPHIC DESCRIPTIONS. 
The oil shales on which the following descriptions are based have all 
received some official consideration during the war period as possible sources 
for the production of liquid fuel. 
The samples that have been chosen for petrological study are believed 
to be fairly representative of the various deposits. 
K 
