ANNIVERSARY ADDRESS. 43 
the passages previously quoted, and is due to the geological struc- 
ture of the district, as will be presently shown. 
(2) The plain between Lapstone Hill and the coast consists for 
the most part of low undulating hills with smooth outlines, seldom 
attaining an elevation of five hundred feet above the sea, and 
chiefly composed of clay-shales with strips of alluvial ground. 
Near the coast, however, the physical features characteristic of 
the Blue Mountains reappear on a smaller scale, in the shape of 
bold cliffs and deeply eroded bays and estuaries. The cliffs attain 
an elevation of from one hundred to two hundred and fifty feet. 
The southern, western and northern portion of this area is drained 
by South Creek and the Nepean and Hawkesbury Rivers, while 
the eastern is drained by George’s River and the Parramatta 
River. 
(3) The continental shelf stretches from the coast eastwards to 
the one hundred fathom line in a tolerably uniform slope of about 
thirty feet to the mile. From. the edge of the continental shelf 
the sea-bottom descends rapidly to a depth of 2,300 fathoms. 
[See Plate 2, diagm. 1.] 
2. Geology—A. Formations.—(1) Sedimentary.—a The 
Devonian. Rocks belonging to this formation are exposed at 
the base of the western escarpment of the Blue Mountains from 
Capertee to at least as far south as Hartley. They consist chiefly 
of quartzites, in which the brachiopods Spirifera disjuncta and 
Rhynchonella pleurodon abound, and the lamellibranch Pteronites 
Pitimani is not infrequent. The presence of Lepidodendron Aus- 
trale in these rocks was proved by Mr. J. Clunies-Ross, B.Sc, and 
by Mr. Pittman and myself in 1894.1 
These rocks graduate upwards into sandy argillites containing 
Lepidodendron Australe in tolerable frequency. Both have been 
strongly intruded by granite, as is well shown on the section which 
accompanies Mr. C, 8. Wilkinson’s geological map issued by the 
1 Rep. Austr. Assoc. Adv. Science, Hobart, 1892, and Rec. Geol. Sur. 
N.S. Wales, Vol. r11., pt. iv., pp. 194-201. By Authority, Sydney, 1894. 
