50 T, W. E. DAVID. 
so charcteristic of this portion of the mountains, the outcrop of 
this thin bed at once catches his eye in the face of the opposite 
cliff, shewing as a thin red horizontal line about halfway up the 
cliff face of yellow sandstone. Near the great Zig-zag, above 
Lithgow, the Narrabeen Beds have a total thickness of 357 feet; 
traced eastwards they thicken considerably, until at the Cremorne 
Bore their thickness amounts to 1,897 feet. The progressive 
thickening of these beds, especially of the chocolate shales, is 
shewn on diagram 1, Plate 2. Between Sydney and Bulli, about 
five hundred feet above the level of the Bulli seam, are some gritty 
and shaly beds, greenish-purple or reddish-purple, containing flakes 
and minute veins of metallic copper. These are known as the 
cupriferous tuffs and have been described by me elsewhere.* 
There can be little doubt that these purple shales, as well as 
the chocolate shales, represent volcanic tuff deposited in water, 
and that the metallic copper is derived from the decomposition of 
basic minerals in the tuff beds. It may here be mentioned that 
metallic copper occurs in minute veins in a basic lava contempor- 
aneous with the Permo-Carboniferous system at Shoalhaven in the 
Illawarra district. Pebbles of quartz-felsite, quartzite, etc., from 
two to four inches in diameter may frequently be observed in these 
beds near the coast, probably derived from the continental shelf. 
Calcareous sandstones, shewing Fontainebleau sandstone structure 
may also be seen in these beds near the coast.” 
2, The Hawkesbury Sandstone. This division appears to be 
conformable to the preceding in the Blue Mountains, though there 
is evidence of a certain amount of contemporaneous erosion along 
their junction to the north of the Hawkesbury River. Near 
Mount Victoria, in the western division of the Blue Mountains, 
the sandstones have a thickness of about two hundred and fifty 
feet, they are there capped by a bed of pale greenish-grey clay- 
1 Rep. Austr. Assoc. Adv. Science, Sydney, 1887, Vol. 1., pp. 275 - 290. 
— Cupriferous Tuffs of the Passage Beds between the Triassic Hawkes- 
bury Series and the Permo-Carboniferous Coal-measures of N.S. Wales.” 
2 Journ. Roy. Soc. N. 8S. Wales, Vol. xxvit., 1893. 
