338 FLORIDA GEOLOGICAL SURVEY SIXTH ANNUAL REPORT. 



' 20. EAST COAST STRIP. 



(figures 87-90) 



References. Curtiss, Harper i (226), Leeds; Matson & Sanford (155-166), 

 Mayer (858, 864, 865-868). Illustrated in 2nd Ann. Rep., pi. 7.2; 3d, pi. ii.i, 

 14.1, 17.1; 4th, pi. 3.1, 11.2; 5th, pi. lo.r, 13.1. 



The coast of Georgia is bordered by low sandy islands, behind 

 which are salt marshes several miles wide, intersected by an in- 

 tricate system of crooked tidal channels. The same sort of coun- 

 try extends into Florida, gradually narrowing, until in the southern 

 part of St. John's County it is reduced to little more than a straight 

 sandy beach strip not over a mile wide, sometimes with a narrow 

 lagoon behind it, and sometimes connected with the mainland. This 

 coast strip covers probably not more than 200 square miles in Nas- 

 sau, Duval and St. John's Counties. 



Geology and Soils — The beaches and outermost dunes are com- 

 posed of cream-colored sand of Recent age, mixed with a varying 

 proportion of shell fragments. Usually the shell material is hardly 

 noticeable, but near the north end of Anastasia Island, and at vari- 

 ous places farther south, it makes up almost the whole of the mass, 

 and is more or less cemented together (especially on the surface), 

 forming a sort of rock called coquina. More sand is continually 

 being washed up on the beach and piled by the wind into dunes, but 

 at a distance of 100 yards or so from high-water mark it is prac- 

 tically motionless. The dune sand that has been stationary for 

 many years is usually nearly white, probably on account of 

 the leaching out of the soluble material (as was suggested in con- 

 nection with the West Florida coast strip). There are no salaman- 

 ders or gophers on the islands to counteract the leaching, and other 

 subterranean animals (other than fiddler-crabs in the marshes) are 

 probably scarce. The soil of the salt and brackish marshes, as in 

 similar situations in other states, is a very impure peat or muck, 

 with a somewhat sulphurous odor. Neither mechanical nor chemical 

 analyses of any of the soils are available, but the dune sand, espe- 

 cially that of the older dunes, must be very poor in soluble minerals, 

 while the marsh muck is probably just the opposite. 



Topography and Hydrdgraphy — The beaches are generally 

 very smooth, firm and straight, so that they make good paths for 

 automobiles. The dune areas, both modern and ancient, are charac- 

 terized by a very wavy or knobby topography, with pretty steep 

 slopes in some places and a maximum elevation of perhaps 25 feet 



