.4 Contribution to the Geologic History of the Floridian Plateau. 135 



As the basis of an estimate of the total solids removed annually from the 

 interior, let it be assumed : (i) that the average total solids in spring water amounts 

 to as much as 219 parts per 1,000,000, this average being obtained from 8 of the 

 typical large springs of central Florida; (2) that the annual escape of the under- 

 ground water approximates the annual intake, amounting, as previously estimated 

 (p. 16), to 460,536,689 gallons per square mile. Upon these estimates the mineral 

 solids removed amount to a little more than 400 tons annually per square mile. 



Of the minerals thus removed, calcium carbonate or limestone greatly pre- 

 dominates, exceeding the combined weight of all other minerals. From the analy- 

 ses it appears that magnesium carbonate, magnesium and calcium sulphates are 

 present in variable, although usually limited quantities. Chlorides are normally 

 present in small amount, although occasionally, as in the case of Perrian Spring, 

 they are exceptionally high. Silica is present in amounts varying from 5 to 25.5 

 parts per 1,000,000. Traces of phosphoric acid and of iron and alumina are usually 

 present. 



The several undetermined factors which enter into the above estimates of 

 mineral solids removed make it difficult to formulate a concrete statement of the 

 rate of lowering of the general surface level. Nevertheless, such statements are 

 desired and have a comparative value. Assuming for the rock removed, most of 

 which is limestone, an average specific gravity of 2.5, a layer a foot thick over a 

 square mile should weigh about 2,166,666 tons. The calculated rate of removal 

 of this rock is about 400 tons per square mile per year. From these estimates it 

 would appear that the surface level of the central peninsular section of Florida is 

 being lowered by solution at the rate of a foot in 5,000 or 6,000 years. (Prelim- 

 inary Report on the Underground Water Supply of Central Florida, Florida Geol. 

 Surv., Bull. No. 1.) 



When an attempt is made to estimate the amount of calcium car- 

 bonate borne into the sea by the waters of southeastern Florida, the diffi- 

 culty is immediately encountered of no analytical records having been 

 kept of the waters ; therefore any estimate must be based upon a com- 

 parison with other regions, and the result obtained in those regions is of 

 doubtful applicability to the one under discussion. Sir John Murray ' 

 averaged the analyses of 19 rivers and obtained the result that 326.710 

 tons of CaC0 3 per cubic mile of water were discharged into the ocean. 

 The quantity per cubic mile in southeastern Florida may be somewhat 

 greater. Therefore it is suggested that the amount of this material 

 poured annually into the bays and sounds of this region may be between 

 400,000 and 500,000 tons, or about Y0V0 of a cubic mile of limestone. 

 This amount of material spread over the floor of the. bays and sounds 

 after a considerable proportion has drifted seaward would give only a 

 thin coating for each year. 



PRECIPITATION OF CHEMICALLY DISSOLVED CALCIUM CARBONATE. 



The problem of the precipitation of the CaC0 3 in solution after it 

 has been carried into the sea presents itself. The only definitely known 

 process by which this may be accomplished is by the expulsion of the 

 CO,. This may be brought about by several methods: it may be driven 

 off by the heat of the sun, it may be lost by the agitation of the waters, 

 or extracted by marine plants. As it is not likely that the surface of the 

 sea is heated to a higher temperature than that of the land, mechanical 

 agitation and the action of marine plants are considered the most prob- 

 able causes of precipitation in Florida waters. 



1 Scottish Geograph. Mag., vol. in, pp. 76, 77, 1887. 



