A Contrihiition to the Geologic History of the Floridian Plateau. 127 



ically removing to it a portion of the deposit. The sand of southern 

 Florida has attracted the attention of a number of geologists, among 

 them Professor Shaler and Mr. A. Agassiz. The material must have been 

 derived from the continental masses to the north, but the various factors 

 by which it was brought so far south have not been thoroughly understood. 



GEOLOGIC DISTRIBUTION OF SILICEOUS SAND IN FLORIDA. 



Until recently the amount of sand in the geological formations under- 

 lying the surficial Pleistocene deposits was not known. Therefore it may 

 be interesting in this connection to outline the geologic history of arena- 

 ceous deposits in Florida. The table of geologic formations on the 

 preceding page is taken, with some verbal changes, from "A Prelim- 

 inary Report on the Geology of Florida, with special reference to the 

 stratigraphy, by George Charlton Matson and Frederick G. Clapp, includ- 

 ing a chapter on the Topography and Geology of Southern Florida by 

 Samuel Sanford." ^ 



In northern Florida the following geologic formations older than 

 the Pleistocene contain sand beds: 



Pliocene: Lafayette formation, Alachua clay, Nashua marl, Caloosahatchee 



marl. 

 Miocene: Jacksonville formation, Choctawhatchee marl. 

 Oligocene: Alum Bluff formation, Hawthorne formation. 



In the northern portion of the State formations of every period from 

 the Oligocene to the Recent contain deposits of sand. It should be 

 stated, however, that no predominantly sand beds have been reported 

 from the Vicksburgian Ohgocene, although the formations of that group 

 contain some sand and silica of organic origin. 



In southern Florida sand of Pleistocene and post-Pleistocene age 

 is generally known to be present, at least as far south as Miami. The 

 three following well records extracted from Mr. Sanford's chapter in the 

 report on the stratigraphic geology of Florida will indicate its distribu- 

 tion in preceding geologic periods: 



Partial record of well of C. I. Craigin, Pahn Beach. 



Description. | Feet. 



Sands with thin layers of semi- vitrified sand at 50 and 60 feet o to 400 



Very fine-grained soft greenish-gray quartz sand, containing occasional foraminif- 



era and water- worn shell fragments 400 800 



White sand with abundant foraminifera of four or five species 850 860 



Gray sand, containing shark's teeth, small water- worn shells and bone fragments, 



sea-urchin spines, and lithified sand fragments 904 915 



Samples at frequent intervals, Vicksburg limestone containing Orbitoides in 

 abundance throughout, together with occasional indeterminable fragments of 

 molluscan casts, corals, and echinoderms. It is a creamy white, hard, homoge- 

 neous limestone throughout 1,000 1,212 



* Prepared in cooperation between the United States Geological Survey and 

 the Florida State Geological Survey, under the direction ot Thomas Waj'land 

 Vaughan, Florida Geol. Surv., 2d Ann. Report, 1910. 



