86 FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
THE AREA TREATED. 
The area considered in detail in this report includes the follow¬ 
ing counties: Nassau, Duval, Clay, St. Johns, Putnam, Volusia. 
Orange, Brevard and St. Lucie. This section borders the 
Atlantic Coast for a distance of 250 miles, and comprises the princi¬ 
pal artesian area of the east coast. 
While central Florida, described in the preceding paper on water 
supply* is prevailingly a limestone country, having limestone for¬ 
mations at or near the surface, this eastern section of the State is 
prevailingly a section free from limestones. These differences, due 
primarily to differences in geologic structure, have given rise to 
marked differences in the topography, drainage, soils and water 
supply of the two sections. 
GEOLOGY. 
A knowledge of the geologic structure is essential to a clear 
understanding of the underground water conditions. The prevail¬ 
ingly level country of East Florida renders geologic observations 
difficult. Some favorable exposures occur, however, and these 
together with data obtained from well samples and well records 
permit a reasonably full understanding of the structure of this part 
of the State. 
The geologic periods in eastern Florida in the order of occur¬ 
rence are: Oligocene, Miocene, Pliocene and Pleistocene. Of 
these divisions the Oligocene is the oldest; the Pleistocene the most 
recent. 
OLIGOCENE. 
VICKSBURG GROUP. 
The oldest or deepest formations reached in well drilling in 
eastern Florida are the Vicksburg limestones. The Vicksburg is 
an extensive deposit underlying all of Florida and extending into 
adjacent states. In central peninsular Florida from Columbia to 
Sumter Counties, as described in the preceding paper on water 
supply, these limestones are frequently exposed at the surface. 
Passing to the east from central Florida they dip beneath the surface 
and while nowhere exposed at the surface in eastern Florida, are 
reached by all deeper wells. It is in fact from these limestones 
that the principal water supply of eastern Florida is obtained. 
*Fla. State Geol. Surv. Bull. No. i, 1908. 
