466 NEW SOUTH WALES. 
of the rock. The coats of sandstone in the concentric mass are from 
half an inch to two inches in thickness: they have a fine granular 
texture and a light gray colour; they peel off readily, and some large 
masses have fallen down into the road. The thin walls of the fissure 
project a little, the layers either side having fallen away, owing to 
their less compactness. This is the only instance observed by the 
writer of concretions in the Sydney sandstone on so large a scale; 
and even those of small size are not common. 
In the argillaceous shale near Paramatta, there are fine examples of 
this structure, as is well laid open to view along the river’s edge oppo- 
site that city. ‘The rock is intersected by fissures dividing it into 
irregular polygonal areas, generally not exceeding two feet in dia- 
meter. ‘These fissures, as in the case above described, are bounded 
by walls about a third of an inch thick; and within the areas, the 
concentric structure is neatly developed. The surface of each is a 
portion of a large flattened sphere, approaching the curvature of a 
lunette watch-glass: the layers are thin, (averaging a fourth of an 
inch,) and separable. ‘The rock has a dark colour, and does not differ 
in any apparent characters from the horizontally laminated shale. 
Other particulars respecting this structure are described on a fol- 
lowing page, in our remarks on the inferior formations, where figures 
are given. 
Dip of the Sydney Sandstone.—The layers of this formation are in 
general, as already stated, nearly or quite horizontal. An inclination 
amounting to twelve degrees is very rarely met with, and no instance 
was observed in which this dip was exceeded. 
Near Port Jackson, an inclination to the westward or northward 
and westward is barely apparent. At the North Head it is more dis- 
tinct than at the South, but does not exceed five degrees. Near the 
mansion of A. McLeay, Isq., there is a dip of one and a half degrees 
to the southward and westward. At Paramatta, the argillaceous schist 
along the river dips two degrees to the east-northeast, in which incli- 
nation the sandstone below it partakes. But at the quarries, half a 
mile distant, no dip was apparent. The sandstone of the Illawarra 
range inclines slightly to the westward, or northward and westward. 
Near Greenhills on the Hunter, there is a dip from the valley of the 
river to the southeast or south-southeast at an angle of ten to twelve 
degrees. At Puenbuen, the dip of the ridge to the west-southwest of 
the plain is sex degrees to the west-southwest; other portions of the 
same ridges are nearly horizontal. 
