PR KSI dent's address IV) 



a peneplain of most of Eastern Australia. Since a marginal 

 river would lack the requisite sloj)e to flow 'or carve on a 

 peneplain, those were the days of radial drainage , when 

 such a river as the Hunter might perhaps have risen at 

 Cobar, and a river in the place of the Shoalhaven mighl pos- 

 sibly have run from Forbes. The coast would have extended 

 then for some distance seawards of the present position. The 

 Thomson and the Carpenter Deeps, though already in exis- 

 tence, had not attained their present depth or breadth and 

 had lapsed into a state of inactivity. 



A new cycle, the present, was inaugurated by the de- 

 velopment of energy in the Thomson and Carpenter Deeps. 

 "The master movements are," say Chamberlin and Salis- 

 bury, 'the sinking of the ocean-basins."* A strip of un- 

 sunken shelf off Cape Capricorn now lies wedged between the 

 peripheries of the two ocean basins. Only at this corner has 

 radial drainage survived. Within its range of action each 

 deep has replaced radial by marginal rivers. Undulations 



Fig. 8. — Diagram of transition from radial to marginal drainage. In 

 the back ground llie former peneplain is represented as extending further 

 seaward tlian the present land and as continuing in a broad continental 

 shelf. Recent folding is shown as having crumpled and sunk the former 

 shelf and shore, and as having intercepted former streams by a littoral 

 ridge. Former rivers now reversed are supposed to be eroding the inner 

 portion of the peneplain. 



(Fig 8) pulsating from these abysses are considered to have 

 broken back the coast line and ridged up ranges in the 

 coastal districts of New South Wales and Queensland respec- 

 tively. The drainage systems of the preceding peneplains 

 were thereby broken, their upper waters being reversed and 

 directed to another coast and their lower portions being re- 



Chamberlin and Salisbury : (ieology i., 1904, p. 520. 



