lM>S Dahj — Pleistocene Glaciation and Coital Reef Prohlem. 



eitlicr in areas of elevation or in areas of long-continned crustal 

 repose ; tliono-li Ajjjassiz acconnts for the depth of certain 

 laii'oons and channels thron<>-h local, very moderate suhsidence. 



In tlie literatnre of coral reefs there is no systematic discus- 

 sion of another possihility which must fmidamentally affect the 

 theory of coral reefs; namely, a positive movement of sea-level 

 in the coral-reef zone of the earth, independently of crustal 

 subsidence. The writings of Suess have now made this idea 

 very familiar, and few geologists will be disposed to deny the 

 validity of the principle. In the following pages the attempt 

 is made to show that the melting of the Pleistocene glaciers in 

 both northern and southern hemispheres resulted in a slow, 

 relatively small, but tlieoretically important raising of sea-level 

 throughout the intertropical zone. Most of the plateaus from 

 which annular and barrier reefs rise are credited to Pleistocene 

 marine erosion operating on Tertiary islands, shoals, or conti- 

 nental shores. The corals colonized those plateaus during late 

 Pleistocene time and have since continued the reef growth. 

 The atoll and barrier-reef forms were inevitable consequences 

 of the late Pleistocene drowning. 



This conception thus seems to supply a missing link in the 

 chain of argument used by Semper, Rein, Murray, Agassiz, and 

 Guppy against the wholesale-subsidence hypothesis. Darwin 

 and Dana depended very largely on the visible forms of coral 

 reefs in constructing their ingenious theory. If it can be 

 shown that these forms were produced by increase of ocean 

 water in the equatorial zone, the hypothesis of enormous crustal 

 deformation beneath the coral archipelagoes is shorn of its 

 strongest argument. 



In one instance the writer has been successful in the search 

 for earlier statements of the relations between Pleistocene gla- 

 ciation and the forms of coral reefs. After describing evi- 

 dences of the recent drowning of most islands and coasts, Penck 

 writes : " The causes of the general rise of sea-level in the latest 

 geological time might perhaps be connected with those cli- 

 matic changes which the eartii underwent in the Glacial period. 

 If, during that time, northern Europe, northern North Amer- 

 ica, and the Antarctic regions were simultaneously glaciated, a 

 considerable mass of water must have been removed from 

 the ocean, and, if the thickness of ice be assumed as ],00() 

 meters, the sea-level must have been 150 meters below its pres- 

 ent position." * The context of this passage gives no explana- 

 tion of the flatness and nearly uniform depth of the plateaus 

 on which the visible i-eefs have been built. Partly for this 

 reason, Penck's suggestion has not received, in the recent writ- 

 ings on coral reefs, the attention it deserves. In any case, it is 

 * A. Penck, Moi-phologie der Erdoberflaeche, vol. ii, 1894, p. 660. 



