GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 323 



The manner of producing the result is subordinate to the result. 

 However the conditions may be brought about, preexistent flats 

 and gradual submergence are two factors needed to supply continu- 

 ously favorable conditions for the growth of reef -forming corals. 

 The importance of deglaciation on modern coral-reef development 

 consists in its having caused a gradual and moderate increase in the 

 depth of the ocean, thereby producing submergence both in rate 

 and amount favorable for the growth of reef-forming corals. 



The general conclusions here expressed are similar to those pre- 

 viously published in a number of my papers. Before discussing the 

 bearing of my conclusions regarding the formation of coral reefs on 

 the theories advanced by others, I will give brief attention to some 

 remarks by Prof. W. M. Davis. The following paragraph is copied 

 from a paper by him entitled: The origin of coral reefs. 1 Similar 

 remarks occur in others of his papers. 



Reefs and Reef -Platforms. A modification of Darwin's theory has lately been 

 proposed by Vaughan, who regards recent submergence proved by the embayments of 

 the central islands as the determining cause for the upgrowth of existing barrier reefs 

 but who interprets the deeper and larger part of the entire reef mass as an independent 

 "platform" of earlier origin. As this investigator has not yet published his views 

 regarding the origin of the reef-platforms his modification of Darwin's theory will not 

 be here discussed further than to note that it seems inapplicable to many barrier 

 reefs in the Fiji and Society groups; that the discontinuity of certain barrier reefs 

 seems to be explicable on the assumption of imperfect upgrowth during and after 

 a recent and rapid subsidence as well as on the assumption of independent origins for 

 the reefs and their platforms; and that, while the extension of reef-platforms outside 

 of the coral zone as in the case of the Great Barrier reef of Australia, truly suggests a 

 dual origin of reef masses, this does not exclude the contemporaneous growth of plat- 

 form and reef within the coral zone during long-continued but irregular or intermittent 

 subsidence. 



Most of the objections raised by Professor Davis have been an- 

 swered on preceding pages of this paper. It will be obvious to those 

 who have read what I have said that my inferences as to submergence 

 are by no means confined to the evidence of embayments in shore 

 lines. In fact, many submerged areas show no clear-cut shore-lice 

 embayments. It will also be obvious that the interpretation I am 

 making did not originate with me. E. C. Andrews, in 1902, after his 

 work on the Great Barrier reef of Australia, put forward in essential 

 principles the same explanation. 



In answer to Professor Davis's statement '"'regarding the origin of 

 the reef platform," I will say that the recognition of the fact of super- 

 position does not require knowledge of the constitution or origin of 

 the basement on which an object or structure has been superposed. 

 We may recognize the fact that a book lies on a table without knowing 

 the kind of material of which the table is composed or the process of its 



1 Nat. Acad. Sci. Proa, vol. 1, pp. 146-152, March, 1915. 



