^4 Contribution to the Geologic History of the Floridiaii Plateau. 107 



with the Key Largo Hmestone. A well on Old Rhodes or Elliott Key 

 might give the desired infonnation. 



Probably a number of years will elapse before these deficiencies 

 in the information on the geology of Florida will be supplied, as tedious 

 and protracted research is necessary. It is hoped this paper may serve 

 as a convenient summary of the present knowledge of the geologic 

 history of this interesting region, perhaps present an interpretation 

 somewhat different from those preceding, and be a stimulus to further 

 investigation. 



TOPOGRAPHY OF THE FLORIDIAN PLATEAU. 



That the land surface of Florida represents only about half of the 

 area of the Floridian Plateau has been known for a number of years. 

 A. Agassiz has called attention to it in his "Three Cruises of the Blake " ' ; 

 Shaler, in his "Topography of Florida"^; Dall, in his "Neocene" Corre- 

 lation Paper ^; and Sanford in his "Topography and Geology of Southern 

 Florida."^ 



RELATION OF THE 100-FATHOM CURVE TO THE PRESENT LAND 

 SURFACE AND TO GREATER DEPTHS. 



The loo-fathom curve, which is considered the delimitation of the 

 continental shelf, lies between 85 and 90 miles offshore, east of Fernan- 

 dina; south of this locality it curves gently and gradually approaches 

 the shore, until opposite Fort Lauderdale it is less than 5 miles distant. 

 It follows closely the seaward face of the main line of the reefs, curves 

 to the westward, passing between 10 and 15 miles south of Key West, 

 about the same distance south of the Marquesas, and 20 miles south of 

 the Tortugas, beyond which it bends to the north of west. The width 

 of the Plateau along the 25° of latitude, which passes through Florida 

 Bay, is between 240 and 250 miles. Just south of its intersection of the 

 25° parallel it takes a slightly curving course to the north of west and 

 lies about 45 miles south of Pensacola. (See plate i.) 



The width of the Plateau along different parallels is given in the 

 following table: 



Width of the Floridian Plateau along Parallels of Latitude. 



Parallel. 



Total 



width, land area. 



Ten miles south of St. .\ugustine . 



29° 



28° 



27° 



26° 



miles. 

 40 s 

 33 5 

 310 

 297 

 266 

 242 



West of 



miles. 

 205 

 180 

 130 

 130 

 160 



225 



Land area. 



miles. 

 135 

 115 

 140 

 145 

 100 



East of 

 land area. 



miles. 

 6s 

 40 

 40 



1 Distance across Key Largo. 



» Vol. I, p. 152, 1888. 



* Mus. Comp. ZooL, Bull., vol. 16, p. 139, i8go. 

 'U. S. Geol. Surv., Bull. 84, p. 86, i8gi. 



* Florida Geol. Surv., 2d Ann. Report, p. iSo, 1910. 



