548 A STRIKING EXAMPLE OP RIVER-CAPTURE, 



the head waters of the Shoalhaven formed part of the Wollondilly 

 system, flowing along the plateau of approximately the same level 

 as the latter stream. If this were so, there should be distinct 

 evidence of the former course in the configuration of the country. 

 This is found to be distinctly the case. The maps (fig.l and 

 Plate xlii.) show that a well defined channel exists, extending 

 from Digger's Creek in a general north-north-westerly direction 

 past Glen Rock Trig. Station and between Marulan and Shepherd 

 Trig. Stations, leading from the valley of the Shoalhaven across 

 the trend of Barber's Creek to Joaramin Creek. There is a 

 gentle fall all the way from the precipitous northern bank of the 

 Shoalhaven to the point of entry into the Wollondilly system. 

 This valley is not by any means the chief evidence available. 

 On the very edge of the precipitous bank of Digger's Creek, 1,500 

 feet above the present stream, there are extensive remains of a 

 very coarse river- gravel. The boulders in this run up to two 

 feet in diameter (Plate xliii., fig.l). They include fragments of 

 granite, quartzite, slate, black jasper, quartz porphyry and other 

 rocks which do not occur anywhere in the valleys of the streams 

 now draining from north to south in this neighbourhood. The 

 boulders are perfectly rounded and mostly show evidence of long 

 transport. They are quite similar to the rocks lying away to 

 the south, and therefore within the scope of action of the ancestor 

 of the Shoalhaven. It is inconceivable that this gravel should 

 have accumulated upon the very edge of the precipice where it 

 now occurs, and, in fact, forms part of that precipice. The deep 

 gully of Digger's Creek and that of the main river must be of later 

 date than the river-gravel. 



We have followed this gravel more or less continuously for a 

 distance of over three miles as shown on the map (Plate xlii.). 

 In places it is covered by a thick capping of sandy alluvial 

 washed down from the surrounding hills. Towards the north- 

 western end of the channel this later alluvial completely hides 

 all trace of the gravel; but there can be no other outlet for the 

 stream that brought the gravel, except that indicated, namely, 

 the gap between Marulan and Shepherd Trig. Stations. The 



