DEPARTMENT OF MARINE BIOLOGY. 237 



not brought out by the soundings. West of Vestal Shoal the sea-bottom 

 drops suddenly from 10 to 20 fathoms, with a flat or gently sloping surface 

 between 20 and 28 fathoms. South of Coalbin Rock there is an escarpment 

 between 10 and 30 fathoms, a flat or gentle slope between 30 and 40 fathoms, and 

 another flat or gently sloping area between 40 and 50 fathoms. The soundings 

 are not sufficiently numerous to trace surfaces with a feeling of confidence, 

 but the scarp from 10 to between 25 and 30 fathoms is clear cut and can be 

 followed for 25 miles to the west end of the Quicksands. Westward, in the 

 vicinity of Tortugas, besides the bottom of Tortugas Lagoon and the surface 

 of the shoal 7 to 10 miles west of Loggerhead Key, there are two undersea 

 terrace plains; one is at a depth of 15 to 17 fathoms; the other (which is a large 

 plain west of the Tortugas) ranges in depth from 28 fathoms on its landward ta 

 36 fathoms on its seaward edge and has an east-and-west width of 10 miles. 

 The 15 to 18 fathom flat is especially well developed south and southwest of the 

 Tortugas. It is separated by a scarp from the 28 to 36 fathom flat, and by 

 another scarp from the shallower levels in the Tortugas. 



The presence of the continuous scarp from Coalbin Rock to a point off the 

 west end of the Quicksands, with a depth of 25 to 30 fathoms at its base, 

 and the presence of a terrace flat 28 to 36 fathoms deep, 10 miles wide, and 

 bounded on its landward margin by a similar scarp, suggest that the portion of 

 the Florida reef tract west of Key West at one time may have stood some 20 

 fathoms higher than now; while the 15 to 18 fathom terraces suggest another, 

 shallower stand of sea-level.^ 



Although the tracing of the oscillations of the Florida reef tract can not 

 now be made in detail, it seems probable that the tract at one time stood more 

 than 120 feet higher than at present, and in the submergence which has 

 followed the land area has been greatly reduced. Besides the problematic 

 larger swing, there have been intermediate stands of sea-level and numerous 

 minor oscillations. The last movement of importance was one of submer- 

 gence, but subsequent to it there has been a minor uplift of some 10 feet or 

 sUghtly more in the vicinity of Miami. 



In order to round out this account of the development of the reef corals 

 and coral reefs in Florida and the southeastern United States as regards their 

 relations to changing position of sea-level, the table on page 238 is taken from 

 a paper by Vaughan.^ As the stratigraphic relations of all the formations con- 

 taining reef corals or coral reefs in the area mentioned have been studied, the 

 conditions with reference to changing sea-level are known. 



This table shows that all the important developments of reef corals in the 

 area considered have taken place either during or subsequent to submergence. 

 Vaughan's studies in the West Indies and on the Caribbean and Gulf shores of 

 Central America have shown that the relations there are similar; and by com- 

 bining data obtained by others in the Pacific area with the results of his own 

 investigations, he has reached the conclusion that all important offshore reef& 

 investigated have formed during or subsequent to submergence. 



Because of the widespread interest in the subject, the bearing of the results 

 obtained through the investigation of the coral reefs of Florida and the West 

 Indies on coral-reef theory, especially the Darwin-Dana hypothesis, will be 

 briefly stated. The hypothesis mentioned postulates not only subsidence but 

 also a method of building platforms behind the reefs by a process of infilling 

 and leveling. The reefs and platforms are supposed to grow upward simul- 

 taneously. As regards the relations to subsidence, or upward growth during 

 or after submergence, the facts available are in accord with this hypothesis; 

 but as regards the development of the marginal platforms they are not in accord. 



'Compare these with Vaughan's statements on pp. 370—373. 



^Abstr., Science, n. s., vol. 41, pp. 508-509, 1915; Bull. Geol. Sci. Amer., vol. 26, pp. 58-60, 1915.. 



