WATER SUPPLY OP EASTERN AND SOUTHERN FLORIDA. 175 
lower level than at present, permitting the ocean to extend inland 
some distance beyond the present coast line. Conrad* has re- 
*Conrad, T. A., Am. Journ. Sci. (2) 11, 38, 1846. 
corded the occurrence of marine shell deposits of post-Pliocene 
age along the banks of the St. Johns River at an elevation of 
from ten to fifteen feet above the present high tide. Conrad also 
reports a similar post-Pliocene deposit about one-half mile from 
the bank of the river near the ancient village of PTasard. Marl 
deposits are said to occur near the mouth of the St. Johns River, 
on the banks of Ft. George Inlet. That the depression of the 
coast during Pleistocene time was general is indicated by the 
records from several other localities. 
Beneath the Pleistocene, Pliocene deposits probably occur over 
some parts of the county. The total thickness of the Pleistocene 
and Pliocene, if both are represented, is, however, not great, as 
the fossiliferous Miocene limestone was reached at Jacksonville, 
in the boring at the city well, at a depth of 33 feet. 
AREA OF ARTESIAN FLOW IN DUVAL COUNTY. 
The area of artesian flow in Duval County is indicated on the 
accompanying map by shading. As will be observed the flowing 
area borders the Atlantic coast, Nassau and St. Johns Rivers 
and extends some distance inland, following each smaller stream 
and tributary. The wells in western Duval County are non¬ 
flowing. A topographic map of this section would assist in deter¬ 
mining flowing and non-flowing sections, since the flow is to a 
large extent correlated with elevation. It is to be borne in mind, 
however, that artesian water depends primarily upon the struc¬ 
ture of the underlying formations and these formations are liable 
to variations of which there is no surface indication. For this 
reason, while the map indicates the area of probable flow the 
exact limits of the area are best determined by drilling. 
