166 Papers from the Marine Biological Laboratory at Tortugas. 



that the material was largely brought from the north by alongshore 

 currents, moving toward the south and southwest. This was not a 

 cold but a warm return or countercurrent similar to the one now moving 

 southward along the Florida east coast. 



EVENTS ABOVE SEA-LEVEL. 



Important events were taking place on the land on which fluvial 

 and lacustrine deposits were accumulating, while the marine history 

 outlined in the foregoing remarks was being enacted. As this paper is 

 especially devoted to the marine history of the State, the episodes con- 

 fined to the land surface will not be recounted. They may be found in 

 Dall's chapter on Florida in the Correlation Paper, "Neocene," 1 by him 

 and Harris, and Matson and Clapp's Preliminary Report on the Geology 

 of Florida. 2 



UPLIFT AT THE CLOSE OF THE PLIOCENE. 



Toward the close of the Pliocene deposition the Plateau mass again 

 began an upward movement, as was evidenced by the shoaling in the 

 Caloosahatchee area and the formation of fresh-water ponds. This 

 upward movement continued until extensive areas of the Pliocene sea- 

 bottom were lifted above sea-level. 



PLIOCENE-PLEISTOCENE INTERVAL. 



The history of this interval unfortunately is not so clear as is desir- 

 able. The shoaling of the Pliocene sea and the rise of former sea-bottom 

 was made evident in the preceding paragraph. Data are deficient for 

 a definite estimate of the amount of the emergence. 



Professor Shaler, because the Vicksburg limestone has lost its salt 

 water to a depth of a thousand feet, postulated an elevation of at least 

 that amount. 3 Matson in criticism of this conclusion says: 



The deep wells all penetrate the limestones of Vicksburg age, and hence it is 

 the beds of that age which have been drained of salt water. As a portion of these 

 beds have been above sea-level since Oligocene time, the salt water may have been 

 removed before the Pleistocene. The magnitude of the emergence is not necessarily 

 so great as 1,000 feet, because, given the necessary chance for escape, the salt 

 water would probably be displaced by fresh water, provided the surface was high 

 enough to afford a small hydrostatic pressure. The absence of impervious beds 

 of clay above the submarine portion of the Oligocene limestones would permit the 

 escape of the water, and hence considerable thicknesses of the older rocks may 

 have been filled with fresh water without being raised much above their present 

 altitude. (Florida Geol. Surv., 2d Ann. Report, p. 169, 1910.) 



Two other probable criteria are left. The first is the existence of 

 underground channels from which submarine fresh-water springs issue 

 near the coast. The best known of these springs is one near St. Augus- 

 tine. Matson and Clapp furnish the following account of it: 



According to Captain E. C. Allen of that city [St. Augustine], the orifice of 

 the spring is about 60 feet across and the depth is about 200 feet. The depth of 

 the sea at the point of emergence is said to be about 50 feet and the water emerges 



1 U. S. Geol. Surv., Bull. 84, pp. 127-131, 1892. 



2 Florida Geol. Surv., 2d Ann. Report, pp. 133-145, 167, 1910. 



3 Bost. Soc. Nat. Hist., Proc, vol. xxiv, p. 584, 1890. 



