THE GEOLOGY OF MITTAGONG. Syl 
of greenish quartzites. Next 5 yards of a fine grained 
rock, followed by 70 yards of shaley sandstone showing 
well marked prismatic structure. A clear junction with 
the next rock a coarse dolerite, can be seen, trending 60° 
east of north. The dolerite contains small zeolites, 
probably natrolite. Lower down the rock contains square 
pieces of shale. Twenty yards further a decomposed cliff 
of very basic black rock occurs. This has altered on the 
surface to a greenish-grey powder and weathers into 
spheroidal boulders. A section of rock obtained from 
centre of a boulder shows it to be a picrite containing much 
magnetite and pyrites. On the southern bank is a high 
bluff (75 feet) of rock with granitic texture but which turns 
out to be a kaolinised dolerite. (See Section IV., No. 9.) 
eller Gk 
Out rop f, A 
Fig. 8.—Section C D (see fig. 6). 
IV. PETROLOGICAL DESCRIPTIONS.’ 
This section is accompanied by microphotographs of four 
of the most interesting rocks of the district, see Plate 26. 
The chief type of each group of rocks will be described 
petrographically in some detail first, and any points of 
interest in other similar rocks then noted. The percentages 
of constituent minerals given are, in the case of the finer 
1 A list of the Rock Sections described herewith will be found at the 
end of this Section LV. 
