GLACIAL-CONTROL THEORY OF CORAL REEFS. 223 



Sea-cut Platforms and Drowned Valleys Outside the Coral Seas. The 

 Glacial-control theory implies a lowered wave-base and a lowered 

 base-level for rivers during much of the Pleistocene period. The 

 objection has been offered that the expected topographic effects are 

 not visible in extra-tropical regions. A reply to the objection is to be 

 found in the world's maps and charts. More than twenty years ago, 

 Penck recognized the abundance of drowned stream valleys along 

 coasts which have not been glaciated or uplifted in Recent time. He 

 referred this widespread phenomenon to a general rise of sea-level 

 and found the cause of the rise in the melting of Pleistocene ice, as 

 several other authors had stated before him. To the same cause he 

 attributed the development of the "Flachsee," which rims the conti- 

 nents and larger islands.^* The general failure of geologists to follow 

 Penck's lead seems to be due to over-emphasis on crustal subsidence 

 as a cause of positive movements of sea-level along shore lines. In 

 many modern works no other condition for positive movements is even 

 mentioned. Examples are plentiful in the state survey and other 

 papers dealing with the Pleistocene and Recent geology of the Atlantic 

 States south of New York. 



The many buried rock-channels of the Thames, Cam, Tawe, Neathe, 

 Wye, Severn, Avon, Dart, Towy, and other rivers in England and 

 Wales, like those found beneath the estuary muds at Milford Haven, 

 Plymouth, and Falmouth, have depths of the order required, if these 

 channels were cut during the Pleistocene time of lowered sea-level. ^^ 

 The Recent submergence of the Dogger bank in the North Sea has 

 been correlated with the drowning of the British valleys. ^^ Other 

 cases of Recent drowning to the same moderate degree are abun- 

 dantly described in the literature concerning the Atlantic coast from 

 Maryland southward. ^^ Erosion while the level of the Gulf of 

 Mexico was Glacially low^ered, may well account even for the buried 

 channel of the lower Mississippi.^^ To turn to the other side of the 

 world, Andrews and others state that the New South Wales coast 



54 A. Penck, Morphologie der Erdoberflache, Stuttgart, 2, 580, 658-660 

 (1894). 



55 W. Whitaker, Quart. Jour. Geol. Soc, 46, 333 (1890); T. Codrington, 

 ibid., 54, 251 (1898), and 58, 35 (1902). 



56 A. S. Kennard, in discussion of J. W. Stather's paper, Quart, Jour. Geol. 

 Soc. 68, 327 (1912). 



57 See particularly G. B. Shattuck's volume on the Pleistocene and Pliocene 

 deposits of Maryland, published by the Maryland Geological Survey (1906). 



58 See J. Leconte, Elements of Geology, New York, p. 558 (1892). 



