A Contribution to the Geologic History of the Florid i an Plateau. 109 



of the mouth of the Apalachieola River. Such a slight elevation would 

 increase the land surface approximately one-third. 



THE REEFS. 



No attempt will be made to give a detailed account of the reefs, as 

 the classic descriptions of Louis Agassiz 1 and Alexander Agassiz 2 are 

 so well known. The reefs occur as a disconnected series just landward 

 of the io-fathom curve, between it and the main line of keys, extend 

 from Fowey Rocks as far westward as the Marquesas, and disappear in 

 the Tortugas. The northernmost living reef known is that at Fowey 

 Rocks. L. Agassiz says 3 "in the immediate vicinity of Cape Biscayne 

 there is a mud shoal, laid partly bare at low water, over which grow 

 branching Millepora, with small tufts of Oculina and Caryophyllia 4 

 rising between them, and here and there a few Porites furcata." 



On the surface of the tongue of land east of the northern end of 

 Biscayne Bay and Virginia Key, I collected wave-tossed, dead speci- 

 mens of the following corals: Cyphastrea hyades, Orbicella annularis, 

 Orbicella cavernosa, Mussa (Isophyllia) sp., Favia fragum, Mceandra 

 areolata. The original source of these specimens was not determined. 



I found living specimens of Siderastrea radians and Porites forma 

 furcata off the northeastern end of Key Biscayne in water from 2.5 to 4 

 feet deep. The living corals do not form a reef, but grow on a sandy flat. 



Professor Shaler's report 5 of the extension of the Florida reef as 

 far north as Hillsboro River is not convincing. An occasional coral does 

 not mean a coral reef; besides " Manicina" areolata is, according to my 

 experience with Florida corals, not a reef coral, strictly speaking. Its 

 habitat is on protected flats. The species cited, when found alone, rather 

 indicates the absence of a reef. 



The water over the reefs is always shoal. The following table, com- 

 piled from United States Coast Survey charts, gives the names of the 

 principal reefs from Fowey Rocks southward, and the depths of water 

 over them. It shows that the reefs occur between water-level at low 

 tide and depths of 18 to 20 feet. The reefs, as already stated, are discon- 

 nected, with passages a few fathoms — usually 9 to 12 feet, always less 

 than 10 fathoms — between them. 



1 Report on the Florida Reefs, Mus. Comp. Zool., Memoirs, vol. vn, 1880. 



2 Three Cruises of the Blake, vol. 1, Chapter m, 1888. 



3 Op. til., p. 16. 



4 Probably Cladocora. 



5 Mus. Comp. Zool., Bull., vol. 16, p. 148. 



