On the Occurrence of the Diamond near Mudgee. 97 



boulders weighing several hundred-weiglit ; thus testifying a 

 strength of current at least as powerful as, if not in excess of 

 the force of the present stream. 



Though the sis localities of Older Pliocene drift, just 

 enumerated, are the principal sources of the diamond, they are 

 not the only ones. At Two-mile Flat it has been found in a 

 younger drift, which we shall provisionally term Newer Pliocene, 

 as it occurs at a lower level, and also contains decomposed 

 pebbles of basalt, which appear to have been derived from the 

 protective covering of the Older Pliocene drift. It is probable 

 too that the diamonds in this drift have been washed out of the 

 older deposit. We shall allude to this further on. 



Many diamonds have also been extracted from the water-holes 

 in the river, but wherever this occurs the Older Pliocene drift 

 has been previously discharged there by the diggers when gold 

 was the only object sought for. Except in such spots the river 

 bed of the Cudgegong has not afforded a single diamond. 



Before describing the general nature and contents of the Older 

 and Newer Pliocene drifts, it will be as well to give a bi*ief sketch 

 of the geology of the Cudgegong bUsin, and of the neighbourhood 

 more immediately surrounding the diamond district ; this will 

 assist in any inferences regarding the original sources of the 

 various materials which compose the ancient river gravels. 



The Cudgegong rises in the acute angle, open to the west, 

 which the Dividing range forms in latitude 33° S., and the first 

 part of its course is N.W. sixty miles. In this part it is bounded 

 on the N.E. by the Dividing range, which presents a summit of 

 horizontal sandstone with various coal seams ; the range in its 

 continuation southwards completely encircles the head of the 

 Cudgegong, and presents a similar formation of Carboniferous 

 rocks. Accordingly we find outliers of Hawkesbury sandstone 

 and underlying Carboniferous deposits, which include G-lossop- 

 teris shales and coal seams, occurring in great force about the 

 upper sources of the river. Several outcrops and cappings 

 of basalt also occur on summits and spurs of the Dividing range. 

 The main area of the basin and the ridges which confine it on the 

 S.E., are of tilted slate and quartzite, with a few fossiliferous 

 limestone bands, which are considered to belong to Upper 

 Silurian or Devonian age ; these are interspersed with small 

 areas of granite, greenstone, quartz-poi*phyry, and felstone. 

 The presence of Calceola in the limestone of Mount Erome, 6 

 miles above Mudgee, may assist in determining the age of a 

 portion of the beds, but it is not improbable that both formations 

 are represented. At Wialdra Creek, where the diamond-drift 

 sets in, the Cudgegong makes a remarkable alteration in its 

 course ; it suddenly bends to the S.W., aud reaches the Macquarie 

 at a point 28 miles distant. This part of its course presents a 



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