all outcrops. Wianamatta shales are exposed on the 

 western and southern side, often considerably hardened by 

 baking. The eastern and northern surfaces are mainly of 

 very much decomposed breccia. This is composed of frag- 

 ments of Hawkesbury sandstone (which underlies the 

 Wianamatta shale at no great depth) and fragments of 

 Narrabeen conglomerate. I have found here a green con- 

 glomerate with pebbles of jasper similar to that occurring 

 at a depth of 2,400 feet in the Balmain Colliery shaft, in 

 the jasper of which Mr. R. S. Bonney has found casts of 

 Radiolaria. 



Blocks of basalt also are plentiful in the breccia, and 

 fragments of the plutonic rocks to be described later, 

 generally in a highly altered condition. The central por- 

 tion of the neck is filled in with a green breccia, perhaps 

 the unweathered equivalent of that previously described, 

 but more clearly of the same character as the breccia tilling 

 the Hornsby neck. At the sharp bend in the old cart track 

 on the eastern side is a mass of grey current bedded sand- 

 stone covered by carbonaceous shales. These appear to 

 have been brought up from the coal measures. Tiiey are 

 broken through by a mass of breccia to the east. On tlie 

 western face they appear as irregular black patches dotted 

 with white rock, and dipping at a high angle. This is the 

 broken up and brecciated equivalent of the horizontally 

 placed carbonaceous beds on the opposite side. The main 

 mass of the basalt breaks through the breccia and formsau 

 oval area some eighty yards long and fifty wide. It has 

 sent many veins into the surrounding rocks as shown in 

 the sketch map ; in particular the breccia is seamed with 

 irregularly running veins, (shown diagrammatically only) 

 and in places seems to have been broken up and recemented 

 by a paste of basalt. The largest basalt vein in the centre 

 of the quarry shows excellent semi-radially arranged 



