DEPARTMENT OF MARINE BIOLOGY. 233 



Oscillation of the Florida Coral Reef Tract. 



As in the opinion of many students of the coral-reef problem, the essential 

 part of the coral-reef theory lies in the relation developing reefs bear to changes 

 in position of sea-level and in the role played by corals as constructional geo- 

 logic agents, these two subjects should receive particular attention from all 

 investigators of the problem. The former subject for the Florida area will here 

 be dealt with in detail, and the latter briefly considered. The latter has 

 received much attention from Vaughan, and additional information is given 

 in Vaughan 's report in this Year Book. 



The oscillations of the Florida reef tract have been discussed in most detail 

 by Sanford and Vaughan. According to the latter, who has summarized the 

 data accumulated by Sanford and himself, also those gathered farther north 

 in the peninsula by Matson, Clapp, and others, the character of the Florida 

 coast-line shows that the last important movement of the peninsula was down- 

 ward, that the keys participated in the uplift and subsequent depression that 

 affected the mainland, that they at one time stood more than 30 feet higher 

 than they now do, and that this uplift and subsequent depression, according to 

 all available evidence, extended to the Tortugas.^ In the last Year Book of 

 this Institution, p. 232, Vaughan stated regarding the Tortugas: 



"Studies of the bank around Loggerhead Key showed the bottom to be composed of rock, 

 which is frequently bedded, and whose surface is pitted, jagged, cavernated, and tunneled, 

 with a zone of imdercutting, the upper edge of which ranges in depth from 16 to 24 feet 

 . . . previous observations combined with additional somewhat casual observations 

 strongly suggest submerged surfaces which were sculptured at or above the reach of the 

 waves, while wave-cut cliffs occur at lower levels." 



In the same Year Book he pointed out evidence of minor uplift subsequent 

 to submergence in the vicinity of Miami. Bearing in mind the previous work, 

 an endeavor was made to procure as much supplemental information as pos- 

 sible and all evidence was critically reviewed. As lands of low relief and 

 underlain by porous and easily soluble limestone, such as southern Florida, do 

 not have conspicuous valleys, no assistance in interpreting oscillations was ex- 

 pected from this class of phenomena. The lines of evidence found usable were 

 (1) scarps and terraces, both above and below sea-level; (2) submerged solution 

 wells and caves; (3) submerged peat deposits; (4) submerged indurated rock. 



The physiography of the land and sea-bottom in the vicinity of Miami were 

 studied in considerable detail. The following will give an idea of the features 

 there exhibited: (1) An upland plain stands at an altitude of 17 to 20 feet, 

 and in South Miami is separated from the next lower plain by a sea-cut escarp- 

 ment, approximately 10 feet high. (2) This next lower plain is the one on 

 which most of the city of Miami is built. The general altitude of its surface is 

 about 8 feet, but it rises toward Biscayne Bay and in Palm Park a part of it is 

 between 10 and 11 feet. The gentle rise is probably due to an old beach ridge. 

 This plain occurs at the base of the scarp in South Miami and is separated by an 

 obscure scarp from the next lower terrace. (3) The third terrace from the 

 top should perhaps be grouped with the second. The altitude of its surface is 

 between 4 and 5 feet, and it stands above a lower bench (4) which has an alti- 

 tude of 1 to 2 feet. 



Miami River has trenched its channel into the Miami oolite to a depth of 

 about 18 feet below sea-level. 



Borings in Biscayne Bay, to ascertain the nature of the foundation for 

 piers, have revealed the presence of a terrace east of INliami 10 feet below low 

 tide. The records of these borings were reported by Mr. John Mills, engineer 

 of the Anton Dohrn. The submerged terrace extends across Biscayne Bay, 

 and upon its surface has been built the sand spit on the east side of the bay. 



'Jour. Wash. Acad. Sci., vol. 4, p. 29, 1914 ; Carnegie Inst. Wash. Pub. Xo. 182, pp. 63-65, 1914. 



