crust, smoother and less permeable 

 than the porous crust and marked 

 by the absence of root tubes; 

 and (3) microcrystalline rind, a 

 thin, dense, tan microcrystaline 



calcite mosaic. Figure 30 illustra- 

 tes the mechanisms responsible for 

 forming subaerial crusts formed on 

 the Florida Keys. 



REPRECIPITATION OF: Dissolved 

 CaCCU to form laminae &/or 

 lateral migration of fluid 

 over crust surface 



EVAPORATION OF: 



(1) rising capillary CaCO, waters, 



(2) ponded meteoric solutions 

 containing CaCO, leached from 

 bedrock and 



(3) gravity and wind driven drain- 

 age from soil patches (rich 

 in CaCO, and organic material. 



" — — Organic Motter 

 ° ° »° ° Corbonale Particle 

 ;£& "^JtCoCOjSoturated 



s in Soil 

 Water 



Figure 30. Schematic drawing of mechanisms involved in forming 

 subaerial crusts in the Florida Keys (adapted from 

 Multer and Hoffmeister 1968). 



No studies have been found 

 describing the origin and formation 

 of existing freshwater marl areas 

 observed by Alexander and Dickson 

 (1970, 1972) in the Key Deer Wild- 

 life Refuge. Whether these are of 

 marine or freshwater origin is un- 

 known. Davis (1940) describes the 

 succession of mangrove species to 

 climax coastal hammock forests as an 

 accumulation of mangrove and other 



humus with a marl clay, of marine 

 origin, until it becomes granular 

 and loamy and supports the vegeta- 

 tion of the hammock forests. Obser- 

 vations on the soils associated with 

 the Caribbean pine and hardwood ham- 

 mock communities included in more 

 recent studies concur with Davis 

 (1940) (Alexander 1953, Alexander 

 and Dickson 1970, 1972). 



69 



