136 Papers from the Marine Biological Laboratory at Tortugas. 



In the shallow waters near the shore the opportunity for re-solution 

 as the material settles to the bottom is not afforded and the accumula- 

 tion on the sea-bottom of large quantities of amorphous calcium car- 

 bonate, apparently not of detrital origin, is undeniable. The series of 

 samples collected between Miami and Big Pine Key is evidence of this, 

 and additional evidence was obtained by the examination of the surfaces 

 of numerous banks. 



One bank about 2 miles northeast of Pigeon Key and another, the 

 shoal west of the upper end of Long Island, have been built nearly to 

 the surface of the water, and are composed of loose calcareous ooze into 

 which I sank while attempting to walk on them to my knees or slightly 

 deeper. An oar could be pushed an undetermined number of feet into 

 the material. Mr. Sanford informs me that a rod can be forced down 

 10 feet or more. In fact, the depth of this soft material has not been 

 determined. 



WHITE-WATER PERIODS. 



The white-water periods in the Floridian region are famous. One 

 of the early descriptions of them was given by Captain Hunt. 



The tidal currents set strongly across the reef and through the channels be- 

 tween the keys, the flood running to the north and the ebb to the south side of 

 the key crescent. When storms occur, the agitation of the waves extends to the 

 bottom, over the shallower portions of the grand Bank, and stirs up the sand 

 violently. This causes the water to take up and maintain in mechanical suspen- 

 sion such finely comminuted particles as have too little sinking force rapidly to 

 reach the bottom again. The finer the particles the longer will they remain sus- 

 pended, and the very coarse grains will hardly be lifted from the bottom. Between 

 the coarsest and finest are grains of all intermediate sizes, and whether they will 

 be suspended or not depends on the violence of the storm, and their interval of 

 suspension varies with their size and the violence of the waves. It results that, 

 in all storms of much violence, the water over the Florida Bank becomes white 

 with the bottom deposits. In long, severe northers or gales, the water becomes 

 almost milk-white across the whole Bank. This "white water" is a familiar appear- 

 ance, and is one of the sure signs of proximity to the reef. As storms subside, the 

 white sand and mud are gradually thrown down, and the water clears, after a day 

 or two, to its peculiarly delicate transparency. (Am. Jour. Sci., 2d Ser., vol. 35, p. 

 200, 1863.) 



EFFECT OF SEA-SPRAY. 



So far the only kind of chemical denudation considered is that 

 resulting from the surface run-off of rainwater, but there is another kind 

 operative around a considerable portion of the south Florida shores. 

 This is corrosion by waves and sea-spray beating on limestone ledges. 

 Very good instances of this kind of corrosion are seen on the western 

 face of Gun Key, Bahamas, and illustrations from photographs are 

 shown on plate 8, figs, h and c. There are at present no means of 

 estimating the amount of CaCOg derived in this way, but it is probably 

 considerable. 



CALCIUM CARBONATE DERIVED THROUGH SURFACE EROSION. 



A considerable portion of the Miami oolite is soft and more or less 

 pulverulent. The detachment of masses from the surface by uprooting 

 due to falling trees, etc., furnishes an opportunity for running water to 

 wash away considerable quantities of limy matter. A portion of this. 



