270 
Geology oe Sydney. 
end of the process it will be necessary to 
use only flour emery, and to exercise con- 
siderable care, as a few extra rubs may 
destroy the whole preparation. 
7. Any superfluous balsam scattered on the 
slide can be removed by a hot knife, and 
finally by washing in alcohol. Thus com- 
pleted, the slide is labelled, and forms the 
“thin section ” of the petrologist. 
5. When sufficiently thin, the film must be re- 
mounted on an ordinary microscope 
slide. These slides are usually 3x1 
inches or 2 x 1 inches. While still 
on the thick glass on which it was 
ground, the rock slice must be washed 
with a brush (a tooth-brush will 
answer) to get rid of all emery par- 
ticles. It is next washed in alcohol, to 
remove any balsam, into which grains 
of emery may have been forced. 
6. A clean mounting slip is now laid 
on the warm iron plate, and a drop of 
fresh balsam placed in the centre. 
The thick glass, with its film of stone 
adhering, is also heated; a drop of 
old balsam is placed on the rock slice, 
and a thin cover glass gently laid 
upon it. The thin cover acts now as 
a support for the rock slice, and when 
sufficiently warmed the thin cover and 
rock slice may be pushed gently from 
the thick glass on to the new slide. 
While the balsam is still warm and 
Fig. 76.— A Rock the cover glass and thin slice 
Slice prepared and ma y b e moved about to the exact 
mounted for the mi- centre of the slide, or placed in any 
crosoope. desired position, and then allowed to 
cool. 
Basalt Dyke 
Bondi 
Sydney j 
r -\ 
Aug/te. 
OH vine, 
Plagioclase. 
Mag netite. y 
