GLACIAL-CONTROL THEORY OF CORAL REEFS. 221 



assumed by the present writer for the lowering of tropical sea-level. 

 There is no evidence of a much greater depression of Labrador or 

 Scandinavia during the Pleistocene. It is, further, improbable that 

 the depression was compensated only by uplift of the sea bottom. 



If the repeated assertion that an ice-cap cannot be more than 1,600 

 feet (488 m.) thick were true, the foregoing statement of the Glacial- 

 control theory would need essential changes. The reasoning on which 

 the assertion is based, is theoretically faulty, and its conclusion impossi- 

 ble for any one who has seriously reflected on the plain facts of glacia- 

 tion either in the Canadian Cordillera or in the Laurentian-New 

 England region of the east. Martin's recent proofs that in 1892 the 

 Muir glacier had a local thickness of 750 m. and that in 1894 the 

 Grand Pacific glacier was locally more than 900 m. thick, are good 

 grounds for admitting the possibility of ice-caps which are 1,000 m. 

 or more in thickness. 



Restriction of Reef Corals by Pleistocene Cold. It has been doubted 

 that the reduction of ocean temperature was sufficient to kill or 

 greatly weaken the corals on most of the reefs. Until the last year or 

 two, practically all supporters of the Darwin-Dana theory neglected 

 to discuss this point, and assumed a tropical-sea temperature con- 

 tinuously favorable for coral growth. Dana held that the coral-reef 

 period "probably covered the whole of the Quaternary." ^^ The 

 assumption is clearly unwarranted by the facts now known concerning 

 Pleistocene climate, north and south of the equator. The burden of 

 proof is really on those who hold that the winter sea temperature of 

 the coral-reef areas was not 5° to 10° C. lower during the Glacial 

 period than it is now. 



General Crnstal Stability in the Coral-sea Areas. Upholders of the 

 subsidence theory will naturally question that the ocean floor has been 

 undisturbed for a time long enough for the preparation of the reef 

 platforms by erosion and deposition. According to the new theory, 

 most of this work was done in pre-Glacial time. The work demands 

 much of the later Tertiary, as well as the Pleistocene period, and thus, 

 during several million years, the relation of sea bottom and sea surface 

 was not significantly changed. However, such crustal stability is 

 necessarily postulated only for the parts of the coral-sea areas where 

 broad platforms, about 75 m. below sea-level, are now found. For 

 those areas the assumption of prolonged crustal stability, except for 

 minute oscillations, seems absolutely unescapable. All theories of 



53 J. D. Dana, Amer. Jour. Science, 30, 169 (1885). 



