THE SOILS OF FLORIDA. 
15 
having been based on specimens taken from the excavations at the 
city water-works. The formation is probably extensively developed 
in eastern Florida. It is well exposed along Black Creek in Clay 
County, and has been noted as far south as Bock Springs in Orange 
County. To the north of Jacksonville its extent is undetermined. 
Certain exposures along the St. Marys Biver at Orange Bluff and 
at Bock Bluff may represent this formation, although the age of 
these exposures has not been definitely determined. Well drillings at 
Jacksonville and elsewhere show that a formation resembling the 
Jacksonville formation extends to a depth of several hundred feet 
in the St. Johns Valley and along the East Coast. 
The, Jacksonville formation is prevailingly of a gray or buff col¬ 
ored material made up of coarse sand grains, calcium carbonate, 
pebble phosphate, and some clay. The relative amount of these dif¬ 
ferent ingredients varies from place to place. The material from the 
type locality at Jacksonville has a high proportion of calcium car¬ 
bonate with which is included some sand and clay and relatively 
little phosphate pebble, forming a sandy impure limestone, in which 
occasional fossils are found preserved chiefly as casts. The expo¬ 
sures along Black Creek in Clay County are similar to the exposure 
at Bock Springs in Orange County, although the relative proportion 
of pebble phosphate is increased, that along Black Creek having at 
one time been worked for phosphate. The phosphate pebbles in this 
formation are amber colored or black, and are smooth and shiny. 
They vary in size from very small pebbles, scarcely larger than a 
pin-head, to pebbles the size of marbles. In the lower part of the 
formation, as shown by well borings, the sand predominates over 
the calcareous matter, the material becoming a very sandy, calcare 
ous marl. Phosphate pebbles occur throughout the formation to the 
depth of several hundred feet. 
CIIOCTAWHATCHEE MARL. 
The Choctawhatchee Marl consists of gray sandy shell marl in 
which the fossil shells are often excellently preserved. The marl 
was first described from Alum Bluff on the Apalachicola Biver, 
where it is well exposed, lying immediately above the Alum Bluff 
sands. It is also well exposed along the Choctawhatchee Biver in 
West Florida. 
It is difficult to say to what extent either the Jacksonville forma¬ 
tion or the Choctawhatchee marl has affected the soils. When lying 
near the surface the calcareous material, and to a large extent the 
