224 DALY. 



shows a positive shift of level to the extent of about 60 m., since the 

 Tertiary.^^ 



In fact, the more carefully existing coast lines are studied, the more 

 apparent is the correctness of Penck's generalization and the more 

 unavoidable is the hypothesis that most of the world's drowned valleys 

 were submerged because of a Recent, general rising of the ocean's 

 surface. 



Drowned Valleys of the Coral Islands. Many volcanic islands sur- 

 rounded by barrier reefs have partially drowned erosion valleys. 

 Dana regarded such valleys as proofs of crustal subsidence and Davis 

 has adopted the same view. Some of the island embayments may be 

 correctly explained in this way. For example, New Caledonia and 

 the Fiji archipelago are generally regarded as located in a region of 

 continental fragmentation. During the Tertiary period the eastern 

 part of the Australasian continent was much faulted and otherwise 

 deformed; the already dissected region sank below the sea and many 

 valley bottoms became covered with water, scores or hundreds of 

 meters in depth. Such submerged portions of the valleys were par- 

 tially filled with detritus and shelly material. In some instances, 

 abundance of mud doubtless prevented the sealing of the bays by 

 coral growths. The outer stretches of these bays were thus subject 

 to aggradation by waves coming in directly from deep water. The 

 aggraded parts of the l)ays would have depths of from 20 m. to 50 m. 

 below the sea-level of that time. Very slight additional erosion during 

 the Glacial period, when sea-level was lowered, would be necessary 

 to account for present depths below sea-level. Farther up the bays, 

 the weak materials of the Tertiary deltas were attacked by the Pleis- 

 tocene waves and the sediment thus stirred was dragged out into deep 

 water by currents, both tidal and wind-driven. 



Many of the Fijian and other islands have been uplifted since the 

 time of continental fragmentation; their Tertiary drowned valleys 

 were similarly subject to cleaning-out by marine action during the 

 Glacial period. 



Drowning of the resurrected valleys is a final, expected result of the 

 late-Glacial rise of sea-level. (See also page 227.) 



However, a similar explanation cannot be admitted for most of 

 the coral archipelagoes. These lie outside of the Fiji-New Caledonia 



59 E. C. Andrews, Proc. Linn. Soc. New South Wales, Part 3, p. 786 (1903); 

 C. A. Siissmilch, An Introduction to the Geology of New South Wales, Sydney, 

 p. 153 (1911). 



