GLACIAL-CONTROL THEORY OF CORAL REEFS. 163 



duced in the sea surface by the gravitative attraction of an ice-cap 

 like that covering the northern part of North America in Pleistocene 

 time.* 



The lowering of general sea-level by the abstraction of water from 

 the sea, to form one or more ice-caps, and the corresponding rise chie 

 to melting of the ice have been discussed by some of the authors men- 

 tioned. In 1882, Penck estimated that the Pleistocene glaciation in 

 the northern hemisphere alone sunk the general sea surface 66.5 m. 

 below its present level, assuming that the Antarctic ice-cap was then 

 as large as it is now. If that cap were then non-existent, the Pleisto- 

 cene sea-level would have been about 50 m. below its present position.^ 

 Von Drygalski calculated that the rise of general sea-level chie to 

 melting of the Pleistocene ice-caps has been 150 m., a value later 

 adopted by Penck. ^ 



After the publication of the writer's first paper (1910), Professor 

 D. W. Johnson kindly drew his attention to Belt's statement of the 

 relation between such shifts of sea-level and the origin of coral reefs. 

 As this appears to be the earliest published remark on the subject, it 

 is worthy of "quotation: "Another class of phenomena, usually as- 

 cribed to a gradual sinking of the earth's crust, but which might also 

 be produced by the return of the sea to the level it stood at before the 

 Glacial period, is that connected with the growth of coral islands. 

 Darwin's celebrated essay on their formation first proved that they 

 were due to the gradual deepening of the water. Dana, closely 

 following Darwin in his theory, estimates that this deepening of the 

 ocean bed from which the coral islands rise has been at least 3,000 

 feet, and that the subsidence to which he ascribes it extends round one 

 fourth of the earth's circumference in the Pacific, being indicated by 

 atolls in that ocean for 6,000 miles in length and 2,000 in \\idth." '^ 



Four years later Upham briefly referred to the same theme. After 

 showing that the ocean was diminished as a whole by the growth of 



4 J. Adhemar, Revolutions de la mer, Paris, p. 28 (1840) ; J. Croll, Climate 

 and Time, London, p. 368 (1875); W. Thomson, Phil. Mag., 31, 305 (1866); 

 J. H. Pratt, ibid., 31, 172 (1866); D. D. Heath, ibid., 32, 34 (1866); W. Upham, 

 Geology of New Hampshire, Concord, 3, Part 3. pp. 18 and 329 (1878); A". 

 Penck, Jahresbericht, Geog. Ges. Miinchen, 6, 76 (1881), and Jahrbuch, Geog. 

 Ges. Miinchen, 7 (reprint), p. 31 (1882); H. Hergegell, Gerland's Beitraege 

 zur Geophysik, 1, 59 (1887); E. von Drygalski, Zeit. Ges. Erdkunde, Berlin, 

 22, 274 (1887); R. S. Woodward, Bull. 48, U. S. Geol. Survey (1888). 



5 A Penck, .Jahrbuch, Geog. Ges. Mimchen, 7 (reprint), p. 29 (1882). 



6E. von Drygalski, Zeit. Ges. Erdkunde, Berlin. 22, 274 (1887); A. Penck, 

 Morphologie der Erdoberfliiche, Stuttgart, 2, 660 (1894). A. R. Wallace, 

 in Island Life, London, p. 157 (1880), briefly refers to the principle. 



7 T. Belt, Quart. Jour. Science, 11, 450 (1874). 



