SYDNEY SANDSTONE. 465 
few inches below there is another similar case. To the right there are a few elong- 
ated coaly impressions, four and five feet long. Cavities in this layer contain masses 
of soft clay, some of which (a) are six inches long, 
G. 23 feet.—Blue-black argillaceous shale ; extends to the right, gradually narrowing. 
H. 24 feet.—White sandstone, argillaceous and schistose, crumbling ; loses the most of 
its argillaceous character to the left, still is distinctly marked with horizontal lines 
of deposition about an eighth of an inch apart, and the lamine are separable. 
I. 5 feet.—Argillaceous sandstone; fragile; above, horizontal planes of deposition, in 
lower part, oblique. 
K. 2 feet.—White argillaceous. 
L, 4 feet.—Sandstone similar to the upper layers, more or less discoloured by iron. 
It is observed, in this section, that even layers but three or four 
inches thick are composed, independently of the large layers in which 
they are contained, of oblique layers; and the changes are frequent 
and various. Another example of the structure of these layers is 
shown in the view taken at the South Head of Port Jackson (p. 467). 
The inclination or dip of these oblique layers, in the vicinity of 
Port Jackson and Paramatta, is almost invariably to the northeast- 
ward. I have observed some instances of different directions in other 
parts of the colony, but as far as examined, they are uncommon. 
The amount of dip varies from fourteen to twenty degrees, but usually 
it is quite uniformly eighteen degrees. 
Concentric Structure.—A concentric structure is of much rarer oc- 
currence in this formation than in the coal series and sandstone below. 
One remarkable example of it was observed along the road from Wol- 
longong, ascending the Illawarra range, about two-thirds up the ascent. 
A fissure bounded by parallel walls, two inches thick, here intersects 
the rock nearly vertically, having a small inclination to the eastward. 
Hither side of this fissure and its walls, the sandstone is concentric 
in structure, the two concentric areas being about twenty feet in 
diameter. The figure here given represents the general character 
117 
