GEOGRAPHICAL UNITY OF EASTERN AUSTRALIA. 443 



(a) The Hawkesbunj.— This stream is about 330 miles in 

 length ; its eastern course is only about 40 miles in length, 

 and for the greater portion of its length the stream main- 

 tains a course parallel to the coast. From its source it 

 flows for some distance on a broad plain or valley about 

 2,000 feet in height. This valley may be seen stretching 

 to the north far beyond Wollondilly and the Bullio Trigono- 

 metrical Station toward Burragorang. At Bullio the plain 

 is 2,500 feet in height, and the southern continuation of 

 the Jenolan horst forms the western wall of the great 

 upland valley or plain. Near Wombeyan, however, tiie 

 river has entrenched itself in the upland valley to the extent 

 of 2,000 feet or more. The northerly course of the stream 

 is continued through the Hawkesbury sandstone plateau ami 

 alongside of the monoclinal fold of the Blue Mountains 

 described by David. 1 Older river gravels may be seen on 

 the escarpment. Near Penrith the river leaves the sand- 

 stone in a deep V-shaped notch, and enters upon the Emu 

 Plains and the Wianamatta shales. At this point the river 

 is only a few feet above sea level. After hugging the fold 

 just mentioned for some distance the stream suddenly 

 leaves the low-lying Emu Plains and enters a dense sand- 

 stone plateau about 700 feet in height. This it traverses 

 in a defile. It is just after disappearing into this mass 

 that the remarkable bend of the river is entered upon, by 

 which it alters its long northern course for an eastern one. 

 During the whole passage of the sandstone plateau the 

 base of the river valley is submerged. The canon in places 

 appears to be of the "valley in valley" type. 



Remarkable as this bend of the lower river appears to be, 

 it is still more so when considered in conjunction with the 



