THE ARTESIAN WATER SUPPLY OF EASTERN FLORIDA. 
137 
ville, at which place the Vicksburg is reached at approximately 
five hundred feet from the surface. The wells at Jacksonville, the 
deepest of which reach a total depth of something over a thousand 
feet, do not so far as the records show pass entirely through the 
Vicksburg. 
The formations lying above the Vicksburg are less characteris¬ 
tic lithologically and are not easily differentiated. The surface 
deposits include both recent and Pleistocene material. During a 
part of Pleistocene time this section of the state stood at a lower 
level than at present, permitting the ocean to extend inland some 
distance beyond the present coast line. Conrad* has recorded 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 Hasard. 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 Pleis¬ 
tocene 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-flow¬ 
ing. A topographic map of this section would assist in determining 
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 structure of the underly¬ 
ing 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. 
*Conrad, T. A. Am. Journ. Sci. (2) n, 38, 1846. 
