36 president's address. 



formed to constitute the existing coastal rivers. Perhaps some 

 large estuaries of small streams relate to the reception of 

 greater radial rivers cut off recently. By rapid elevation of 

 intervening ridges, some streams were trapped and forced 

 into lengthy and roundabout covirses. These are now gradu- 

 ally escaping from their bondage, and cutting more direct 

 channels to the sea. 



If in the future there should be a long period without 

 earth movements, it seems reasonable to expect that the 

 cycle will run its course, that the crooked rivers will gain a 

 straighter way to the sea, and that their head waters will 

 reach further back into the interior. But the excavation now 

 being performed by the western rivers would prevent the 

 coastal streams from extending as far back as I assume that 

 they did at the conclusion of the jDrevious cycle. 



The ultimate cause of these earth-movements is beyond 

 the limits of this address. Contraction of the outer crust by 

 secular cooling has been generally accepted as an explana- 

 tion. Lately Professor Chamberlin has suggestei that 

 periodic compressive movements might be due to a shrink- 

 age of the centrosphere and not the lithosphere. Still more 

 recently Dr. Bailey Willis has advanced the hypothesis that 

 such movements had their origin in the tendency of the 

 heavier sub-oceanic segments of the earth to spread and 

 underthrust the margins of the continents. 



Summary. 



Last year's consideration of the deep abyss, described as 

 bordering this part of the continent, concluded witli the hypo- 

 thesis that it i-epresented a pressure-trough. Tn support, it was 

 arcued that its confio-m-ation, and certain features of New 

 Zealand and New Caledonia, whence the pressure was supposed 

 to have come, were in conformit}-. 



Such conditions should leave signs not only in the dii-ection 

 whence pressure came, but also in the direction upon which 

 pressure leaned, namely, tlie East Coast of Australia Tt is now 

 advanced that the crooked and abnormal rivers, so peculiar a 

 feature of this coast, are a consequence of that cause. 



