180 Papers from the Marine Biological Laboratory at Tortugas. 



South of the latitude of the present southern end of Lake Okee- 

 chobee, Hmestones were the prevalent geologic formations, and in this 

 region the four limestone formations of south Florida were formed, all 

 in shallow water. On the southwest it was the Lostman River limestone ; 

 along the southeastern and southern margin coral reefs grew and formed 

 the Key Largo limestone. Behind the Hne of reefs was a channel com- 

 parable to the Hawk Channel of present time. East of the Lostman 

 River hmestone, in shoal water, agitated by strong currents, the Miami 

 ooHte accumulated. Whether this oolite was formed previous to the 

 formation of the Key Largo limestone, or whether the two are contem- 

 poraneous, is an unsolved problem. Westward of the Key Largo lime- 

 stone, oolite was forming on a shallow bank, later to form the group of 

 keys from the Pine Keys to Boca Grande. 



The temperature of this portion of the ocean and the direction of 

 the currents were practically as to-day. 



Pleistocene time was closed by an upHft of the Plateau — the uplift 

 evidently being accompanied by deformation, as the elevations of the 

 surface of the marine Pleistocene are by no means the same. Those in 

 the central portion of the Peninsula are greater than toward the south, 

 and the east coast is higher than the west. There is evidence of a shght 

 ridge on each side of Lake Okeechobee, the eastern ridge being the 

 higher. 



J. O. Wright, Supervising Drainage Engineer of the Department of 

 Agriculture, in a report embodied in the Report of the Special Joint 

 Committee of the Legislature of Florida on the Everglades of Florida,' 

 gives the mean water-level in the Okeechobee Lake as 20.5 feet above 

 tide, level at low stage about 19 feet; the greatest depth at low water 

 is 22 feet, or the bottom is 3 feet below sea-level; the average depth is 12 

 feet, or the bottom is 7 feet above sea-level. Heilprin says concerning 

 the depth of the Lake: 



We took numerous soundings all along our course, probably fifty or more, 

 which gave an average depth ranging from about 7 to 10 feet. The deepest sound- 

 ing made on the diagonal connecting Taylor Creek and the mouth of the canal, 

 about 4 miles southwest of Eagle Bay, gave 15 feet, but this is the only instance 

 when we obtained this depth. (Wagner Free Inst, of Sci., Trans., vol. i, p. 41,1887.) 



Accurate geologic information on the bottom of the Lake is scanty, 

 but as it is surrounded by marine Pleistocene, the surface deposit on the 

 bottom may be safely inferred to be Pleistocene. As Pleistocene occurs 

 at higher elevations on both the east and west sides, the conclusion is 

 pointed that the Lake lies between gentle anticlines, one toward the 

 east, the other westward, and there may have been somewhat gi^eater 

 elevation between its southern end and the southern shore than in the 

 area of the Lake itself, producing a shallow synclinal hollow. 



In the vicinity of Kissimmee the amount of elevation was 60 to 70, 

 or perhaps 100 feet; of Miami, 40 to 50 feet; along the coral reef keys, 

 10 to 15 feet; along the Caloosahatchee, near Fort Thompson, perhaps 

 30 to 40 feet; near Osprey, less than 30 to 40 feet; along the keys west 



' Tallahassee, Florida, 1909. 



