52 
FLORIDA STATS GEOLOGICAL SURVEY. 
are characterized by an abundance of Orbitoides mantelli and other 
foraminifera associated with many other fossils/ prominent among' 
which are Pecten poulsoni and P. perplanus. At the type locality, 
(Marianna, Jackson County) this limestone is so soft that it can be 
cut into blocks with a saw. It contains some beds of chert and many 
of the fossils are silicified. Lithologically, the rock at Marianna re¬ 
sembles the Ocala limestone at Ocala and the “Peninsular” limestone; 
but it differs from the former in the character of its fauna, especially 
in the absence of nummulites, and it is believed that it may represent 
a horizon below the “Peninsular” limestone of Dali. The close lith¬ 
ologic resemblance between the Marianna limestone and the “Peninsu¬ 
lar” limestone, however, makes it possible to combine much of the 
discussion concerning these two formations. 
MARIANNA AND “PENINSULAR” LIMESTONES, 
Stratigraphic Position:—The base of the “Peninsular” limestone 
is not exposed in Florida and there is no satisfactory evidence that it 
has been reached in drilling wells; hence the character of the sub¬ 
jacent formation is not known. Reference has already been made to 
the uncertainty concerning the exact correlation of the “Peninsular” 
limestone of Florida. It will thus be seen that no satisfactory con¬ 
clusions can be drawm concerning the relation which the “Peninsular” 
limestone bears to the underlying beds. The relation of the Peninsular 
limestone to the overlying formations will be discussed in connection 
with those formations. 
The Marianna limestone is thought to be the stratigraphic equiva¬ 
lent of the upper part of the bluff at Vicksburg, Miss., and some of 
the wells in west Florida enter beds of sand and clay which probably 
represent older horizons; but the stratigraphic relation of the forma¬ 
tion to these older beds cannot be determined. In west Florida, where 
this formation is recognized, it is unconformably overlain by beds be¬ 
longing to the Apalachicola group or by post-Pliocene formations. 
Lithologic Character: — The Marianna and “Peninsular” forma¬ 
tions consist of soft, porous, white or light-gray limestone, sometimes 
resembling marl, especially when partially decomposed. Some bands 
of darker-colored, dense limestone are reported at various localities 
where these formations have been penetrated by drilling, and nodules 
and layers of chert are common throughout them, but chert beds are 
especially prominent in certain horizons. The chert beds are usually 
darker in color than the limestone and range in thickness from a frac¬ 
tion of an inch to twelve or fifteen feet. In some localities as many 
as six or seven successive beds of chert have been encountered in a 
single well. In general, the heavier layers are more persistent; and it 
