SANDSTONE BELOW THE COAL 489 
passes gradually into layers, in which no traces of curved surfaces 
can be detected, showing that the hard siliceous texture of the firmer 
layers has arisen from the influence of silica deposited from solution. 
The concentric structure is also well seen at Harper’s Hill on the 
Hunter. It is confined to the upper layer, in which the concretions 
have the form of a flattened sphere, and are from four to six feet in 
horizontal diameter. ‘They consist of concentric layers, which readily 
separate and peel off. In the bed of a stream near Glendon, farther 
up the Hunter, there are other examples, as I am informed, on a mag- 
nificent scale. ‘lhe concretions average ten feet in diameter, and 
cover the surface like artificial domes; in the distant view they look 
like a village of rounded huts. They consist of separable concentric 
coats, and contain seams of quartz or chalcedony, often half an inch 
thick, lying between some of the layers. 
Dip—Fissures— Faults —The dip of the layers in Illawarra is small, 
and varies from one to twelve degrees. In the cliff to the north of 
Wollongong, it amounted to five degrees to the northwestward, and 
increased to ten degrees two hundred yards beyond. In the Wollon- 
gong Cliff, it was two to four degrees; in the cliff north of Kiama, 
three degrees; in Rocky Cove, three miles south of Kiama, three de- 
grees; at Black Head, two degrees; and in each of these cases, as in 
the first, the inclination was to the northwestward. 
Notwithstanding this dip, however, there is a little difference in the 
elevation above the sea, of the layers of rock along the coast south of 
Wollongong. At Shoalhaven, however, nine miles south of Black 
Head, the same layer which lies at the water level of the latter place, 
is found at a height of one or two hundred feet in Mount Coolomgata. 
At Harper’s Hill the rock dips to the northward and westward 
twelve degrees. 
The smaller fissurings of a layer with which a concretionary struc- 
ture is often connected, have no system of uniformity in their arrange- 
ment. There are larger fissures, which are more uniform in their 
courses, and correspond in general to those of the Sydney sandstone, 
though less constant, and not of so frequent occurrence. 
At Wollongong, the fissures vary from northeast-by-north to north- 
northeast. 
At the top of the cliff there is a fissure running northeast-by-north, 
exposing a surface of fracture twenty feet in height. 
At the cliff north of Wollongong Harbour, the course of a fissure is 
east-by-north, and becomes a short distance beyond east and west. 
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