302 FLORIDA GEOLOGICAL SURVEY SIXTH ANNUAL REPORT. 



15. GULF HAMAIOCK REGION. 

 (figures 80, 81) 



References— GiMmore (975), Harper i (222-223, 240, 242-244), Harper 4. 

 Matson & Sanford (413-415), Sellards 3 (294 or 48), Smith 2 (205, 206. 227. 

 234, 235), and U. S. soil survey of Jefferson Co. (by Jones, Thaj-p & Belden, 

 1908). 



This region, which is very distinct from any other, borders 

 the (Julf coast from about St. Mark's to Tarpon Springs. In the 

 area under consideration (i. e., west of Hie Suwannee River) it 

 extends 15 or 20 miles inland, and covers about 1,470 square 

 miles. 



Geology and Soils — The country is everywhere underlaid by 

 hmestone, most of which has been mapped as Upper Oligocene. 

 Outcrops of it a few square feet in extent and projecting a few 

 inches above the surface are very abundant. In some places there 

 may be as many as a hundred such exposures to the acre, and 

 again they may be wanting over several square miles. This rock 

 extends out into the Gulf for an unknown distance, making a 

 rocky bottom in many places. Alternating with the hard rock are 

 unconsolidated beds of marl. The reddish clay that is common in 

 most of the regions previously described is rare here, if it occurs 

 at all. The greater part of the surface material is a more or less 

 loamy sand, a few inches to several feet deep, presumably Pleisto- 

 cene. 



In the drier places the limestone seems to have little or no 

 influence on vegetation; but the swamps, sloughs, low hammocks 

 and damp flatwods contain many plants that are very character- 

 istic, and presumably correlated with the presence of limestone. 

 Neither mechanical nor chemical analyses of the soils are avail- 

 able yet, but the following analysis of marl from a low hammock 

 in Wakulla County, given by Dr. Eugene A. Smith in the 6th 

 volume of the Tenth Census, page 205, is of some interest in this 

 connection : 



'o 



Moisture driven off at 100 C. 1.915% 



Combined water 1.159% 



Carbonic acid 24.253% 



Lime 30.986% 



Magnesia -^ .424% 



Potash -372% 



Soda .338% 



Phosphoric acid .014% 



