318 T. G. TAYLOR AND D. MAWSON. 
Another large area of syenite occurs in the Nattai Valley 
near the anthracite mines, concerning which Jaquet writes: 
“This great mass has forced the strata upward and formed 
a dome, while at the same time sheets have run along the 
bedding planes of the coal measures. One of these sills, 
which has a thickness of over 100 feet has followed the 
roof of the coal seam upon the south side of the valley, and - 
is in actual contact with the coal. The coal is, however, 
comparatively unaltered.’ The syenite sill has decomposed 
into a trap closely approaching kaolin and has been mined 
by local residents. 
1.—b. Trachytes.—A small quarry for local purposes, 
chiefly roadmending, has been opened ina hill about one 
and three-quarter miles from Mittagong, along the Berrima 
road. The rock is a trachyte, and some fine examples of 
columnar structure were to be seen, but have probably 
Since been broken up. The columns are composed of bluish 
rock with a somewhat spotty appearance, and readily crack 
off in large flakes. 
Mount Jellore.—This striking cone rises abruptly out of 
the Triassic sandstones. The south face has slopes of 60° 
and rises sharply up from Jellore Creek. A steep ridge 
runs towards the west composed of quartzites, etc., which 
are intruded by trachyte dykes, especially near the Peak. 
From the Trignometrical Station (height 2,734 feet above 
sea level) a magnificent view northward over the Wollon- 
dilly River can be obtained. The top consists of a fine 
grained greenish rock which is jointed so that the slabs dip 
away from the centre. The lava composing the cone 
appears to have differentiated largely during the process 
of solidification. The summit is composed of a trachyte 
consisting of felspars more or less kaolinised, and irregular 
bunches of blue hornblende, giving a mottled appearance 
to the hand specimen. About 200 feet from the summit 
