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BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



at which it was formed; but 4,000 feet southeast of the cave the 

 elevation is only about 4 feet in amount. I have given more infor- 

 mation on this minor uplift in the paper referred to in the footnote.^ 



Agassiz, Shattuck, and Miller, and I agree as to the geologi- 

 cally Recent submergence of the Bahamas. 



The accompanymg diagram (text-fig. 17) indicates the relations 

 of the barrier reef off the west side of Andros Island to the platform 

 on the edge of which it is growing. This reef is growing on the edge 

 of a platform that had stood above sea level at least as much as 192 

 feet. It was perforated by solution wells and then submerged. The 

 perforations in the platform show that it antedates the barrier reef, 

 and that its formation is not dependent on agencies associated with 

 the presence of the reef. There is here another instance of a reef 

 formed during or after submergence, and superposed on the surface 

 of an antecedent platform. 



— -2-t 



Old oolite 

 dune ridge 



400l 



6001 



eool 



Solution wells 6-7/4fa{homs 



Coral reef Sea l§yeJ. 



Submerged Terr ace |2fms. 



deep through oolite 

 Solution well 31-33 fathoms deep 



JOOfms, 



Horizontal scale 



2.000 4,000 



6,000 Feet 



Fig. 17.— Diagrammatic section across the barrier reef, Andros Island, Bahamas. 



The relative importance of the constructional r61e of the living 

 reef will be briefly mentioned. The Pleistocene oohte of the Bahamas 

 is not coral-reef rock, as was contended by A. Agassiz. It is composed 

 of calcium carbonate chemically precipitated on extensive submarine 

 flats." I have several times published the estimate "that on Andros 

 Island, Bahamas, the ratio of the constructive work of the present 

 reef to that of agencies that previously resulted in the formation of 

 the Pleistocene oolite is approximately as 1 to several thousand, or, 

 as a constructive agent, chemical precipitation has been several 

 thousand times more effective in forming limestone than corals. "^ 



Before passmg to the discussion of the next area it should be 

 pointed out that the amount of submergence of the Bahamas, 228 



J Carnegie Inst. Washington Yearbook No. 13, p. 229, 1915. 



2 For the most recent discussions of this subject, see Vaughan, T. W., Some shoal-water bottom samples 

 from Murray Island, etc., Carnegie Inst. Washington Pub. 213, pp. 277-280, 1918; Chemical and organic 

 deposits of the sea, Geol. See. Amer. Bull., vol. 28, pp. 933-944, 1918. 



3 Wash. Acad. Sci. Journ., vol. 4, pp. 26, 27, 1914; Carnegie Inst. Washington Pub. 213, p. 279, 1917. 



