OCCURRENCE OF PRECIOUS STONES IN N.S.W. 219 
at Bingara, but the stones are on the whole smaller and show a 
higher percentage of “off” colour. 
Summarised, geological conditions of the Cudgegong Diamond- 
field are simple enough. A river valley in Paleozoic rocks, with 
its alluvial deposits, is covered by a sheet of basalt. This basalt 
is again cut through, forming a newer valley and redistributing 
the drifts of the older. The older drift is believed to be Pliocene. 
The redistributed drifts are Pleistocene and recent. Diamonds 
are found in the older drift underlying the basalt, and in the 
redistributed drifts. : 
Bingara.—The conditions under which the diamond is found 
at Bingara are somewhat similar. The geology of Bingara has 
been described by Liversidge, Wilkinson, Pittman, and Stonier. 
The various papers are enumerated in the list of previous 
observers. Shortly, it may be described as an area occupied by 
carboniferous clay-stones, much faulted and broken, serpentine, 
basalt, and Tertiary and Pleistocene drifts. Diamonds have been 
found in the drifts only. These drifts are in places resting on 
the claystones and covered by basalt. Patches of the same drifts 
occur where the capping of basalt has been denuded, and it is in 
areas of this class that the greatest quantity of diamonds have 
been found. The “Monte Christo” mine is a case in point. Here 
the “wash” has been denuded of its basaltic covering and possibly 
redistributed. The surface of the wash is cemented to a hard 
iron-stained crust. Some phenomenal yields of diamonds have 
been recorded from this mine. During my visit, Captain Rodgers 
washed a hundred weight of the drift and got twenty-nine 
diamonds. The gems were small, about three to a carat, and 
nearly half were of a straw colour. 
I measured the following section at a depth of forty feet :-— 
1. Four inches of a wash, of pebbles under half-an-inch in — 
diameter. Glear white and black ‘quartz pebbles, and tourmaline 
Owing. Contains diamonds. 
_ 2. Four feet of wash with pebbles up to three inches in diameter. 
This has gem-sand, but no diamonds. 
