SYDNEY SANDSTONE. 461 
surface, staining the rock to a depth of some feet. Magnetic iron- 
sand is met with along the roadsides and on the sea-beaches. 
This fine variety passes into a grit, and also into a well-characterized 
puddingstone. The grit consists of pebbles of quartz disseminated 
thickly through an arenaceous or sub-ferruginous base. The quartz 
is mostly white, but occurs also of various tints, as red, bluish, green- 
ish, black, &c.; and it is sometimes intermingled with argillaceous 
pebbles. This variety of the rock constitutes thick layers in the 
upper part of the formation. It also occurs in thin patches, extend- 
ing for a few rods between the layers of the finer sandstone. On the 
summit of the South Head of Port Jackson, the upper layer is covered 
in some places for a few yards or rods with these thin patches of peb- 
bles, which appear as if they had been pasted to the surface by 
some process of modern date; but in the face of the cliff, near the top, 
the same may be seen in layers of an inch or less in thickness, 
proving them contemporaneous in formation with the sandstone, and 
a constituent part of it. 
The puddingstone is the upper member of the series. Its peb- 
bles average an inch in size and are often very closely compacted. 
In the valley of the Hunter, near Puenbuen, some deposits consist of 
rolled stones, eight or ten inches through, presenting a variety of 
colours, which give considerable beauty to the rock. They rest on 
a fine-grained sandstone, resembling the Sydney rock. A large pro- 
portion of jasper pebbles with chalcedony, agates, and carnelians occur 
in some beds, as near Harper’s Hill, and the agates are often of great 
delicacy. Ferruginous varieties of both the grit and puddingstone 
are found in many parts of the territory. Major Mitchell mentions 
that they abound through the valley of the Darling. 
A schistose structure is assumed by the rock as the proportion of 
clay increases, and slaty argillaceous layers alternate occasionally 
with the sandstone. The gradual passage of the one into the other 
may be often seen, as at a locality near the residence of A. McLeay, 
Esq. Some thin layers might be properly called a micaceous shale, 
as the slaty structure is wholly due to the mica contained. 
Where the argillaceous layers are most largely developed they pos- 
sess the ordinary characters of such slaty rocks, chipping off in thin 
fragments, and often coarsely crumbling. The colour is the usual 
dull blue-black, or grayish-black. It often passes above to a white or 
grayish-white colour, and the rock then becomes more arenaceous, 
approximating to the sandstone of the region. 
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