130 Papers from the Marine Biological Laboratory at Tortugas. 



CALCIUM CARBONATE OF INORGANIC ORIGIN. 



The calcium carbonate is derived through two inorganic agencies: 

 chemical denudation and erosion. In order to understand both the 

 sources and the means by which the material is transported to the ocean, it 

 will be necessary briefly to consider the geologic formations, topography, 

 vegetation, drainage, rainfall, and surface run-off of the land areas. 



PLEISTOCENE LIMESTONES OF SOUTHERN FLORIDA. 



The whole of the surface of southeastern Florida is either formed 

 or underlain at no great depth by a series of limestones, all of which are 

 of Pleistocene age. The more important of these formations will be 

 described in the succeeding paragraphs. 



The Miami oolite, named from the city of Miami, is a soft, white 

 or cream-colored, oolitic limestone breaking with an irregular fracture 

 and containing streaks of thin, irregular layers of calcite (plate 13, fig. b). 

 The rock is quarried as a building stone in the vicinity of Miami, and as 

 it hardens on exposure it serves its purpose well. Spheroidal oolite grains 

 are its most important constituent. The diameter of the granules ranges 

 from less than 0.5 mm. to a little over i mm. Mr. Sanford, who has 

 studied the granules microscopically, says: 



Examination with the microscope shows that the ovules have a well-marked 

 concentric structure ; the nucleus of some ovules is a rounded aggregate of minute 

 calcite crystals, of others a rounded aggregate less evidently crystaUine; sometimes 

 the nucleus is a shell fragment and frequently it is a grain of quartz. The concen- 

 tric layers vary in number from i to 4 or 5, and in appearance from clear and 

 rather coarsely crystalline to opaque. The layers are darker or lighter from vary- 

 ing amounts of organic matter and amorphous material. 



The oolites are embedded in a cement of amorphous or crystaUine 

 calcium carbonate, and there is some sand. The latter material is more 

 abundant at the north and decreases southward; there is also a slightly 

 greater proportion of sand along the eastern outcrop than toward the 

 west. This formation has a maximum thickness of perhaps 50 feet. Its 

 areal extent is southward from the vicinity of Del Ray to 10 or 12 miles 

 beyond Homestead, and westward it forms the floor of the eastern por- 

 tion of the Everglades. 



The Lostman River Hmestone, named by Mr. Sanford from its typical 

 occurrence along Lostman River, is a non-ooHtic Pleistocene Hmestone 

 of varying physical characters; in some places it is hard, largely made up 

 of crystaUine calcite; in others, soft and friable. At the head of Hender- 

 son Creek it contains considerable sand. Its thickness is said by Mr. 

 Sanford to be 30 feet at Everglade and over 40 feet at the mouth of 

 Shark River. It underUes the shore of the mainland from Jewfish Creek 

 westward and northwestward to near Marco, extends some miles to the 

 north of the last-mentioned place, and to the northeast passes beneath 

 the great swamps of the interior. 



The Key Largo Hmestone is the elevated coral-reef rock forming 

 the main Hne of keys from Soldiers Key to the southern end of Big Pine 

 Key. Its name was taken from Key Largo because of the excellent ex- 

 posures recently made there by the excavations along the Hne of the 

 Florida East Coast Railwav extension. The most conspicuous compo- 



