280 
Geology of Sydney. 
Nepheline, if present, would certainly answer to 
the tests just stated, but a microscopic examination of 
the rock shows that the mineral so readily soluble is 
isotropic. Certain minute clear six-sided forms can be 
found under high powers in every slide ; but this 
mineral, too, is isotropic, and, so far as I can observe, 
no trace of the uniaxial-figure that nepheline would 
show can be seen. 
Hauyne is excluded, as barium chloride gives no 
reaction in a hydrochloric acid solution of the soluble 
portion of the rock. 
We have then an isotropic and easily soluble 
soda-bearing mineral in a rock that gives a reaction 
for chlorine, and contains no sulphuric acid — evidence 
that points to the presence of sodalite in this rock. 
Some of the powdered basalt was gently warmed 
in weak hydrochloric acid (one part of acid to ten of 
water) for two hours. The solution was then evaporated 
to dryness, and repeatedly moistened and almost dried 
alternately for two days. Well-formed crystals of 
sodium chloride were then visible. The whole was 
transferred to a glass slide, and the surplus acid 
removed by introducing the edge of a filter-paper. The 
crystals were then dried on the slide, moistened 
with turpentine, and mounted in balsam. Plate II., 
Fig. 1, is a micro-photograph 1 of the slide. Fig. 2 
shows cubes of NaCI, obtained by etching a square 
inch of surface of polished basalt. The face of 
the slab was just covered with a few drops of strong 
1 These figures may be seen in A T ol. XX., Roy. Soc. New South Wales, 1894. 
