512 W. M. DAVIS SUBSIDENCE OF REEF-ENCIRCLED ISLANDS 



PREVAILING INATTENTION TO REEF CONTACTS 



Various other writers on the islands of the Australasian archipelago 

 have noted the unconformable contacts of elevated reef limestones with 

 the underlying rocks, but few of these writers have emphasized the bear- 

 ing of such contacts on Darwin's theory of coral reefs, and the majority 

 of writers on elevated reefs have paid no attention to the nature of the 

 reef contacts. The unconformity of sealevel reefs, to be considered below, 

 appears to have been even more generally overlooked. Indeed, uncon- 

 formable reef contacts, like embayed shorelines, have no generally recog- 

 nized place in the discussion of the coral-reef problem in standard text- 

 books. These two fundamental principles are, with three exceptions 

 noted below regarding embayed shorelines, not mentioned in the discus- 

 sion of coral reefs in Bonney's Story of our Planet (1893), Credner's Ele- 

 mente der Geologic (1897), Green's Physical Geology (1882), Geikie's 

 Text-book of Geology (1893), Gunther's Lehrbuch der Geophysik (1885), 

 Hahn's Inselstudien (1883), Hann, Hochstetter and Pokorny's Allge- 

 meine Erdkunde (1881), Haug's Traite de Geologic (1907), Jukes- 

 Brown^s Handbook of Physical Geology (1892), Kayser's Lehrbuch der 

 allgemeinen Geologic (1893), Lake's Physical Geography (1915; em- 

 bayments are briefly mentioned), de Lapparent's Traite de Geologic 

 (1906), Leconte's Elements of Geology (1895), Lyell's Principles of 

 Geology (1872), de Martonne's Traite de Geographic Physique (1909), 

 ^eumayr's Erdgeschichte (1886), Penck's Morphologic der Erdober- 

 flache (1891; embayments are briefly considered), Peschel-Leipoldt's 

 Physische Erdkunde (1879), Pirsson and Schuchert's Text-book of Geol- 

 ogy (1915; emba3^ments are briefly mentioned), Prestwich's Geology 

 (1886), Phillip's Manual of Geology (1885), Eichthofen's Fiihrer fiir 

 Forschungsreisende (1886), Scott's Introduction to Geology (1897), 

 Suess' Antlitz der Erde (volume ii, 1888), Supan's Grundziige der 

 physischen Erdkunde (1896), Tarr and Martin's College Physiography 

 (1914), Toulet's L'Ocean (1904), Wagner's Lehrbuch der Geographic 

 (1908), or Walther's Allgemeine Meereskunde (1893) and Einleitung in 

 die Geologic (1893). 



In view of such neglect of essentials, it is not too much to say that the 

 treatment of the coral-reef problem in our text-books is in serious need 

 of critical revision. 



Unconformable Fringing Eeefs 



many fringing reefs testify to subsidence 



The evidence of unconformity, frequently detected in studies of ele- 

 vated reefs, may be found about as easily in the case of sealevel fringing 



