178 Papers from the Marine Biological Laboratory at Tortugas. 



LOSTMANS RIVER LIMESTONE. 



Sanford says concerning the origin of the Lostman River limestone: 



Origin : — Willis has suggested that the rock at Lostmans River was perhaps 

 formed by the deposition of crystallizing calcium carbonate from the presumably 

 limy waters of the Everglades. While there can be no doubt that deposits of marl 

 are now accumulating along the coast, the present hardening of marl to crystalline 

 limestone or the direct deposition of such limestone is not established. As the 

 writer has stated, the bed rock of the western coast, wherever soundings have been 

 made, whether in the Everglades, on swamp islands, along the coast, or in the 

 numerous creek channels, seems to have a gentle slope toward the Gulf. The rock 

 is no farther below water-level in the swamp than in adjacent channels; moreover, 

 the rock surface in channels where the current runs strongly is full of crevices, is 

 extremely rough, and is evidently being eroded. Loose fragments that have been 

 detached by solution are found, not only near the mouths of rivers, but at their 

 heads, on the bare rock, under marl, and under vegetable muck. Another fact 

 that impairs the deposition and crystallization theory is the character of the Ever- 

 glades water. Most of the marl in the Ten Thousand Islands has come from the 

 ever-dirty shallows of the Gulf. The dark limestones below water in the creeks are 

 the same as those that outcrop above water a short distance away, and a recent 

 crystallization from solution of those is hard to understand. 



The limestone on Lostmans River, though containing calcite crystals an inch 

 long, is not greatly different froin other limestones of southern Florida; removal, 

 deposition, and crystallization of carbonate of lime are characteristic of the region.* 



The limestone, from its petrographic and paleontologic characteristics, is a 

 shoal-water deposit of marl and limy sand, containing shells of living species of 

 mollusks, that has been solidly cemented and subjected to conditions favoring 

 crystalline growth. This growth may be in progress. (Florida GeoL.Surv., 2d 

 Ann. Report, pp. 224, 225.) 



KEY LARGO LIMESTONE. 



The Key Largo hmestone is so closely similar to that being formed 

 by the present reefs, that it is safe to postulate the same physical condi- 

 tions for the fossil as for the living reefs. They were formed in water 

 having a maximum depth of 18 to 20 feet, a minimum temperature of 

 70° F., and lay just landward of the current of the Florida Straits. 

 They were separated from the inner bank by a deeper channel, compar- 

 able to the present Hawk Channel, and now represented by the bays 

 and sounds between the keys and the mainland. 



SURFACE SANDS OVERLYING THE MARINE PLEISTOCENE. 



The surface of the Pleistocene fossiliferous deposits is usually 

 overlain by a coating of surface gray or white sand, of variable thick- 

 ness, from a few inches to several feet. Most probably this sand was 

 originally a marine deposit, laid down as the sea shoaled. Wind has 

 been active in distributing some of it over the land surface, as is 

 attested by the dunes of the east coast as far south as Pine Island in 

 the Everglades, back of Fort Lauderdale,^ and on the west coast as far 

 south as Caximbas Pass. 



UPLAND GRAY SANDS. 



The suggestion may be ventured that a portion of the upland gray 

 sandj which covers all pre-Pleistocene formations and has puzzled so 

 many geologists, may be sand of beaches formed as the successive seas 



'For references to calcite crystals in other Pleistocene limestones of Florida, 

 see pp. 130, 131. 



^Florida Geol. Surv., 2d Ann. Report, pp. 224, 225. 



