108 FLORIDA STAT£ GEOLOGICAL SURVEY. 
In Florida the limestonesi clays and sandstones of the Miocene are 
lithologically so unlike the shell marls that in the absence of satis¬ 
factory paleontologic evidence for their exact correlation it "seems 
best to describe them separately: The two 'divisions are> therefore, 
retained, but a new name is given to the. marl. The Scphora bed” 
of Dali is here called the Choctawhatchee marl, from the river in 
western Florida- where it is Welt exposed. At DalLs type locality the 
Jacksonville formation is known only from well records and excava¬ 
tions; hence, the name * is -not entirely satisfactory, 5 However, the - 
Committee on Geologic Names of the H. S. : Geological Survey has 
decided to retain Jacksonville' as the name of the formation because 
(1) it is reasonably well fixed in the literature, and (2) the type fauna 
was collected at Jacksonville. The existence of exposures on Black 
Creek, in Clay County, however, would have led' to-the adoption of 
another name if Jacksonville had not already been used. The samples 
of rock' from wells on the east coast indicate that the limestone beds 
are thin and form Only a minor part of the Miocene in that portion 
of the State ;■ -hence the word formation is here substituted for lime¬ 
stone. ■ 
JACKSONVILLK FORMATION. 
The Jacksonville formation was first recognized by’ Dali, who ob¬ 
tained samples of the rock, together with fossils showing its age, from 
an excavation at the ’ Jacksonville Water Works. 1 
Stratigraphic Position:— L Tlie Miocene beds lie stratigraphically 
between the underlying' Oligocene and the overlying Pliocene and 
Pleistocene formations. From well records and samples obtained 
along the east coast of Florida,-the Jacksonville formation appears to 
rest linconformably- upon the’ eroded surface of the limestones of the 
Vicksburg group at Jacksonville, St! Augustine, and other localities. 
Farther westward, it probably rests on the beds belonging* to the Apa¬ 
lachicola group, but no contacts were Observed. 
Lithologic CharacterWhen fresh, the limestone of the Jackson¬ 
ville formation varies in color from light gray to nearly white, but 
upon weathering it changes to pale yellow of yellowish gray. It 
usually has a porous texture, but occasionally becomes hard and dense. 
The presence of a large percentage of clear quartz sand may be easily 
distinguished by the* use -of an ordinary hand lens,'and microscopic 
examination shows there is also a large amount of clayey material 
which varies in color from light gray to pale yellow. In certain hori¬ 
zons fossils are very abundant, the shells having usually been dis¬ 
solved, leaving nothing but casts or molds; and this fact, together 
1 Dali, W. N., U. S. Geol. Surv., Bull. 84, pp. 124-125. 
