74 FLORIDA GEOLOGICAL SURVEY—FOURTH ANNUAL REPORT. 
THE SAND DUNES. 
The sand dunes, recent and ancient, form by no means an unim¬ 
portant type of country. These are found chiefly bordering the 
coast. Along the Atlantic coast sand dunes are found extensively. 
Near the northern line of the State at Fernandina the dunes border 
the coast, and are forming at present. Passing south, a line of 
ancient and quiescent dunes borders the coast lying from dne-half 
to one and two miles inland, for a distance of 200 miles. When 
formed these dunes probably faced the coast, the land lying then at 
a lower level than at present. A subsequent slight elevation of the 
land having extended the coast line a short distance beyond the 
dunes. Since the elevation, which occurred probably at the close of 
the Pleistocene time, these dunes have become quiescent and are 
now overgrown by a dense growth of vegetation, consisting of spruce 
pine and shrubby plants. At the extreme southern end of the State, 
recent calcareous sand dunes occur. Along the gulf coast of Florida 
low quiescent sand dunes are found bordering the coast in Lee, 
DeSoto and Manatee Counties. From St. Petersburg along the 
gulf coast to Wakulla County the dunes are lacking. This coast 
is chiefly calcareous, representing that part of the coast line in 
which the Oligocene limestones border the coast. The western part 
of the gulf coast from Franklin to Escambia County is a section 
from which limestones are absent and sandy clay formations are 
exposed. Along this coast the sand dunes are again found more or 
less continuously. Those of the mainland are mostly quiescent. 
When originally accumulated the sand of the dunes was probably 
homogeneous, or nearly so. Subsequently under the weathering- 
process a clear line of demarcation has been established between a 
top layer one to four feet in thickness and that which lies below. The 
top layer of sand is light colored or slightly gray near the surface 
from the accumulation of organic matter. At a depth of from one 
to four feet the color changes abruptly to pale yellow. This line of 
demarcation follows the contour of the hill in a cross section of the 
dune. 
On the east border of Lake Kingsley in Clay County is found a 
series of dunes made up of white and unusually well-washed sands. 
SCRUB. 
The native vegetation of the “scrub” is more or less dense, and 
is often almost an impenetrable growth of shrubs or stunted trees 
of various kinds. The top soil is frequently light colored, although 
