president's address. 25 



So in the peneplain epoch, marginal streams being impos- 

 sible, only radial streams existed. If a simple vertical uplift 

 of the ])eneplain occurred tlic rivers would have deepened 

 but not deviated from their former channel. Therefore, the 

 Shoalhawke could not have held its present position in pene- 

 ])lain times, since when the drainage of its area must have 

 radically changed. The long northerly run of that river sug- 

 gests to me that it was banked off from the ocean by the rise 

 i>f jin intervening ridge. This view finds support in the 

 record by Dr. H. I. Jensen* of a monoclinal fold not older 

 than the Pliocene in the Sassafras tableland. I suggest that 

 a fold, rolling before it the bed of a former radial river, 

 commenced at the Kosciusko upland and crept northward till 

 stayed by the resistance of the buttress of the Hvmter. Sul)- 

 sequent deiudation and deformation have altered this littoral 

 ridge, bui the stream it fcu-nied still bears the imprint of its 

 guidance. 



At present the old Shoalhawke valley is fulfilling its 

 natural destiny of being cut across by subsequent streams 

 into blocks of secondary radial drainage. Since a kiUch 

 2)ar(ill('l tf) ihc xea o^>^?o.s"^.>.' tlic rffortx of tiuttcr to cxrape to 

 hiixt h'vt'l hji I lie short e>if irai/, it could he hiif a fciii pornri/ 

 jjhuAc ill yhiixioeira'phii . Hence the old Shoalhawke \ alley 

 itself must be of but slight geological antiquity. 



Mr. E. C. Andrews has already pointed out that the Colo, 

 although the smaller stream, should be regarded as the origi- 

 nal trunk of the Hawkesbury complex. He considered! that 

 its subsequent, a southern tributary, started on a marauding 

 expedition capturing stream after stream until it obtained the 

 Upper Shoalhaven. On the contrary, it is now suggested 

 that the Hawkesbury did not ijrou' out of the Colo, but was 

 driven in to it. If it were so, then the present course of the 

 river would be the ultimate result of abyssal movements. 



* Jensen, Proc. Roy. Soc. N. S. Wales, xliii., 1908, p..102. 

 t Andrews, " Introduc. Phys. (Geography N. S. Wales," 1909, p. 40. 



