38 president's address 



Of wliei'e and what were the rivers of the preceding cycle, the 

 peneplain-times, we have no record. But it is obvious tliat no 

 peneplain could have carried such crooked rivers as the Clarence 

 or tlie Shoalhaven run to-day. Of neces.sity the peneplain-rivers 

 were longer, slower, and straighter than these. They had no fall 

 to waste in that long journey to the sea. On a peneplain, cir- 

 cuitous cour-ses would mean final stagnation. 



The problem is : how were those peneplain-rivers succeeded by 

 an entirely diverse scheme of drainage. The explanation now 

 offered is that these crooked rivers lie in a z<jne of compression. 

 That movements from the pressure-trough threw the coastal area 

 into irregular folds. That these broke and caught the radial 

 rivers, which, turning aside, flowed along their furrows. Then 

 at once denudation played on elevation. Rain and river 

 attacked the higher land and broke it down. At every oppor- 

 tunity the river burst through the obstacle which held it back 

 frf)m the shortest way to the sea. As denudation progres.sed, 

 the river broke through again antl again, until I'achal drainage 

 was restored. Finally the old chamiel, chopped in lengths by 

 cross-streams, appears as an empty river-bed. Every stage in 

 this performance is illustrated by the rivers of New South Wales. 

 There is the Upper Murrumbidgee, newly tilted by earth-move- 

 ments from tlie tSnow\- River. Then there is the Shoalhaven 

 River, both as it was when it ran from the present source of the 

 Tuross to J>roken Bay, and as we find it now. There is the old 

 valley, discovered by Dr. Woohiough, running from >Smoky Cape 

 to Port Stephens; and, lastly, the fragment represented by 

 Jervis Bay. 



It is clear that as these great meridional \alleys, marginal to 

 the coast, are n(jw undergoing rapid disintegration by the 

 ordinary agents of denudation, that thev cannot have endured 

 such attack for long. Consequently these valleys themselves are 

 oeoloyicallv recent. The same conclusion is thus reached as that 

 arrived at through considering;- that these rivers could not have 

 existed under peneplain-conditions, and are, consequently, far 

 younger than the peneplain-period. 



