W. M. Davis — Shaler Memorial Study of Coral Reefs. 247 



killed by any lowering of temperature during the glacial 

 period. Hence if the processes of the glacial-control theory 

 worked alone, unaffected by any subsidence of the ocean bot- 

 tom and its volcanic cones, it is on the borders of the coral 

 zone that their effects should be most visible to-day : or if the 

 glacial-control processes worked in conjunction with continuous 

 ocean-bottom subsidence, it is on the borders of the zone that 

 their combined effects should be most manifest. I had no 

 opportunity of visiting any of the northern- or southernmost 

 coral reefs, except for a brief visit to the Hawaiian island of 

 Oahu, and for a rapid passage across the southern limit of the 

 Great Barrier reef of Australia : it seemed quite impossible to 

 account for the facts that I there observed — or for the much 

 larger store of facts recorded on large-scale hydrographic charts 

 — by the glacial-control theory alone. 



Certain islands in the South Pacific, especially Norfolk island, 

 east of Australia, rise in bold cliffs from extensive shallow 

 platforms, on which a good number of soundings in depths 20 

 or 30 fathoms record "c r 1" (coral) on the bottom. Certain 

 northwestern members of the Hawaiian group, notably Midway, 

 Lisianski and Nihoa islands, rise from similar platforms. It is 

 possible that these extensive platforms may be to a greater or 

 less degree the result of marine abrasion by the lowered and 

 chilled sea of the glacial period, and that the imperfect develop- 

 ment of reefs upon them to-day may be due to rapid submerg- 

 ence that would result, as will be shown in a later section, 

 from the combined action of island subsidence and rising ocean 

 level at the close of the glacial period. But it is the Mar- 

 quesas group at the eastern limits of the coral seas and to-day 

 without barrier reefs, that, according to the scanty accounts 

 available, should present the effects of the glacial-control 

 theory in their most interesting development; for detailed 

 charts show that the embayments of these islands are separated 

 by truncated spurs, such as are demanded by the glacial-control 

 theory, but such as are prevailingly absent in the warmer seas. 

 A special study of that group with particular reference to the 

 several rival theories of coral reefs would be highly instructive. 



The Elevated Reef of Oahu. — Our attention may now be 

 turned to the second group of independent witnesses regard- 

 ing the origin of sea-level reefs ; namely, the reefs of an earlier 

 day now elevated above sea level. It has long been known 

 that the island of Oahn in Hawaii is bordered along part of its 

 shore by an elevated coral reef at an altitude of 20 or 25 feet. 

 The conditions of its origin have been much discussed ; the 

 record of "coral" in borings at a depth much greater than 

 that at which corals can grow has been taken to prove that the 

 reef grew upwards as the island sank ; but Agassiz has pointed 



