120 
FLORIDA GEOLOGICAL SURVEY—I 4 TH ANNUAL REPORT 
PUTNAM COUNTY 
Putnam County is on the St. Johns River, in northeast Florida. In 
the western part of this county the Alum Bluff formation (Miocene) is 
at or near the surface. Exposures of this formation may be seen at 
Grove Park, in Alachua County, a few miles west of the Putnam County 
line. The central part of this county lies in the lake region, and the 
surface formations are Miocene or later. Near the St. Johns River, in 
the eastern part of the county, the Nashua shell marl (Pliocene) comes 
into the section. The regional dip in this county is probably to the east 
or northeast, but is very pioderate in amount. In the western part of 
the county the Eocene probably lies quite near to the surface. On the 
St. Johns River, at Palatka, these limestones, as indicated by well rec¬ 
ords, may be not more than 150 or 200 feet from the surface. At 
Orange Mills, in eastern Putnam County, the Eocene limestones were 
reached at 110 feet from the surface. 
ST. JOHNS COUNTY 
St. Johns County lies between the St. Johns River and the Atlantic 
Ocean, and ranges in elevation from sea level to about 50 or 60 feet. 
The surface in this county is very effectively concealed by sands and 
soil. Only on the coast and on inlets from the ocean have natural ex¬ 
posures been observed. The deposits seen consist of Pleistocene shell 
marls and coquina rock. From well records it is known that the com¬ 
bined thickness of the Pleistocene, Pliocene, if present, and Miocene is 
not more than 200 or 250 feet. At St. Augustine, the Eocene limestones 
are believed to lie not deeper than 224 feet from the surface, and at 
Hastings the Eocene appears from well records to be reached at from 
175 to 200 feet. The record of a deep well drilled at St. Augustine and 
logs of several shallow wells are given in the Fifth Annual Report of 
the Florida Survey, pages 187-196. 
ST. LUCIE COUNTY 
Pleistocene shell marls and sands lie at or near the surface in much of 
St. Lucie County. These shell marls may occasionally be seen in nat¬ 
ural exposures near the coast, but inland the land surface is for the most 
part so nearly level and the drainage courses so little developed that the 
