W. M. Davis — Shaler Memorial Study of Coral Beefs. 233 



Tahiti are truncated by cliffs, some of which are several hun- 

 dred feet in height : and that much of the northeastern side 

 and all of the southeastern end of New Caledonia are strongly 

 cliffed ; but in both of these exceptional cases, the mature val- 

 leys by which the cliffs are interrupted must have been eroded 

 during a relatively long period when the islands stood higher 

 with respect to sea level than they do to-day, and in the rela- 

 tively short period since then the valleys have been submerged, 



Fig. 3. 



Fig. 3. Deduced stages, sectors H to K, of a veneering xeef on a wave- 

 ent platform; sector 0, observed features of a barrier-reef. 



embayed, and more or less filled with delta plains. The ero- 

 sion of the cliffs also must have required a relatively long 

 period of time, and therefore must have taken place while the 

 islands stood higher than now ; hence the base of the cliffs 

 also must have been submerged. The existing barrier reefs of 

 these two large islands must have grown upward during the 

 submergence, in a manner very similar to that in which barrier 

 reefs elsewhere have grown up during the submergence of non- 

 cliffed central islands. Why these two large islands were so 

 strongly cliffed before reefs were formed around them is a 

 problem to which I shall return in my detailed report, though 

 not with great confidence of solving it successfully. 



The Continental Shelf of Australia and the Great Barrier 

 Beef. — Before leaving this explanation of our problem, it 

 should be pointed out that Guppy, in 1890, brought to its sup- 

 port the continuity of the continental shelf, or " submarine 

 ledge " as he called it, along the eastern coast of Australia, 

 from the Great Barrier reef farther southward for a thousand 



