40 
FLORIDA STATE GEOLOGICAL SURVEY. 
SHORE LINES. 
The State of Florida has an extensive coast line, presenting a great 
variety of topographic forms. The various agents which have been 
important in producing the coastal forms are: the waves, the tides, the 
shore currents, and the growth of organisms, chiefly corals. The 
configuration of the shore lines is dependent upon the relative im¬ 
portance of these agents. 
Coral Reefs:—The coral reefs are restricted to an area near the 
southern end of the peninsula; and it was to this area that much of 
the earlier geological work was devoted. In a subsequent chapter Mr. 
Samuel Sanford will discuss the formation of the keys and the ad¬ 
jacent portion of the mainland in the light of his recent studies in that 
region. At present it is only necessary to call attention to the fact 
that coral reefs have been of minor importance in the development of 
the peninsula of Florida; in fact, there appears to be no reason to 
suppose that reefs have existed on the west coast or north of the 
north line of Palm Beach County on the east coast. 
Submerged Continental Border:—Reference to the charts of the 
U. S. Coast and Geodetic Survey shows that the depth of the water 
along* the Florida coast is seldom more than a few feet. As the 
distance from the land increases, the water gradually deepens over 
this submerged continental border and there is an abrupt descent to 
deep sea bottom at a considerable distance from the land. This 
marginal shelf is to be regarded as a part of the continent now covered 
by the sea, and it has probably been in part, if not wholly, above water 
during some period of geological history. 
Bars:—In the shallow water at some distance from the shore, the 
waves gradually build bars which rise nearly to the surface of the 
water. The material for the construction of these bars is derived 
from the sea bottom, and hence they vary with the character of the 
shore. At the present time the prevailing materials on both the east 
and west coasts is sand, though there is often a considerable admixture 
of shells. For this reason the bars which are now forming consist 
largely of sand with a small proportion of shell fragments. In com¬ 
paratively recent geologic time the beach materials on some parts of 
the coast appear to have been largely shells and these were built into 
bars which were afterward cemented to form coquina. Occasional 
layers of sand and a considerable percentage of silica in the coquina 
show that terrigenous material was never entirely absent, though it 
was often of minor importance. In the shallow water along the ex¬ 
posed shores, either of the mainland or islands, currents are formed 
which transport the beach materials and build them into a variety of 
forms. One of the common types to be found on the Florida coast is 
