president's address. 15 



Where one part of an original level sheet is found bent up 

 above and another part bent down below the original plane of 

 deposition, it is a sign of a powerful disturbing force. The 

 valleys of the Blue Mountains and the coast at Sydney indi- 

 cate the rise and fall of the fold to be so fresh as to be pos- 

 sibly still in progress. 



Granting that a fold proves application of lateral pressure 

 then the question occurs from which side of the fold did the 

 pressure come, which was front, which back ? Of a moving 

 wave the steeper side appears in front and the longer slope 

 behind. 



When a stone is thrown into water, undulations recede 

 from the impact, of these the nearer are of greater amplitude 

 than the farther. Seawards of the Sydney-Blue Mountain 

 fold lies the more gigantic flexure of the continental shelf 

 and the abyss. On the principle of the wave of the greater 

 amplitude being nearer to the impulse, these earth folds 

 should be directed from the ocean landwards. 



Mr. A. R. Daly* considers it "a fact that tlie thrust of 

 mountain building has throughout the world been chiefly 

 fi'om the ocean towards the land." And Mr. Bailey Willis 



holds that, "There is abundant evidence to prove 



that the tangential pressures exerted upon the continents 

 proceed directly from the denser submarine masses."! 



As detailed contour surveys in Australia are not available 

 for study, the river systems of the East Coast ai'e here ex- 

 amined. Rivers not only display the present levels, but also 

 to some extent record past movements. 



For the purpose of this discussion the drainage systems of 

 continents may be contrasted as radial or marginal. Usually 

 rivers rise in a central highland and radiate to opposite 

 coasts: this may be described as "radial" drainage. A rarer 

 case is where one coast receives the water from a narrow 

 fringe, here called "marginal drainage," beyond which some 



* Daly. Amer.Mourn. Science, xxii., 1906, p. 212. 

 t Willis, "Research in China," ii. 1907, p.117. 



