GLACIAL-CONTROL THEORY OF CORAL REEFS. 165 



outside that zone, submarine platforms (Pfeiler), on which atolls 

 could originate, are rather rare." ^ 



It was impossible that the ideas of Belt and Upham could be liter- 

 ally accepted, because each implied that the late-Glacial swelling of 

 the tropical seas is to be measured in thousands of feet vertically, to 

 match the Darwin-Dana estimates of shifts of level in the coral seas. 

 Geologists might well be sceptical that the formation of the Pleisto- 

 cene ice-caps could produce an equatorial drop in sea-level of 3,000 

 feet, or more. At the present time even the von Drygalski-Penck 

 estimate of 150 meters seems excessive. It will be noted that Penck 

 offered his suggestion with reserve and he apparently rejected it 

 finally himself, as shown b}^ his later, complete acceptance of Darwin's 

 theory, in a Vienna lecture which reviewed the various coral-reef 

 theories but quite failed to mention Glacial controls. ^° 



So far, the Avi-iter has found no earlier statement of the second, 

 fundamental control of the Glacial climate, namely, that on the 

 distribution of the corals which throve during the Pleistocene. The 

 killing or great impoverishment of the reef-coral fauna, except in 

 small sea areas protected from the comparatively cold water of the 

 open ocean, is believed to be as essential a featiu'e of the Glacial- 

 control theory as the shift of sea-level. 



The writer's 1910 paper was a preliminary note; partly on account 

 of its brevity, the first announcement of the theory has been mis- 

 understood in some particulars. Additional, prolonged study of 

 ocean charts has led to tlie appreciation of many facts, especially 

 quantitative data, which were unknown to the writer when the 

 Hawaiian reef problem was undertaken. These facts seem powerfully 

 to support the new theory and, at the same time, to represent strong 

 objections to the subsidence theory of Darwin and Dana. Both 

 theories postulate a recent rise of sea-level within the tropics, but they 

 are utterly contrasted in their meaning for dynamical geology in 

 general. This paper therefore offers a needed fuller statement of the 

 Glacial controls, as well as an analysis of quantitative elements im- 

 plied in the older theory of submergence. 



9 A. Penck, Morphologic der Erdoberfliiche, Stuttgart, 2, 660 (1894). 

 10 A. Penck, Vortrage d. Verein zur Verbreitung naturwiss. Kenntnisse in 

 Wien, 36 Jahrgang, Heft 1.3, (1896). 



