SECOND ANNUAL REPORT—STRATIGRAPHIC GEOLOGY. 
115 
Section at Jackson’s Bluff, Ocklocknee River. (Continued.) Thickness. 
• Feet. Inches. 
6. Yellow calcareous clay, same horizon Williams fullers earth.. 5 6 
The upper surface of this stratum is extremely irregular. 
There are small channels in it, one is about 5 feet wide 
and more than a foot deep. The basal 6-10 inches of the 
overlying bed are very largely composed of small pebbles 
and in it are imbedded pieces and fragments of the cal¬ 
careous clay. There were apparently cracks in the cal¬ 
careous clay and small pebbles went down into them. 
The contact is distinctly one of erosion unconformity. 
5. Stiff bluish clay .. 6 
4. Calcareous sand. 6 
3. Limestone ledge .• •.• • 2 
2. Greenish sands passing beneath the level of the water in tl^ 
river . 7 
Total ......... . w . 54 
This section is located in the S. W. Sec. 16, T. IS., R. 4 W., 
in a southwesterly bend of the Ocklocknee River. 
The paleontologic evidence indicates a stratigraphic break between 
the Oligocene and Miocene as is shown by the following quotation: 
As I have on various occasions insisted, the faunal gap betweenMie upper¬ 
most Oligocene (Oak Grove) and the Chesapeake (Choctawhatchee) or Miocene 
is the most sudden, emphatic, and distinct in the whole post-Cretaceous history 
of our southeastern Tertiary, and indicates physical changes in the surrounding 
region, if not in Florida itself, sufficient to alter the course of ocean currents and 
wholly change the temperature of the waters on our southern coast. (Wagner 
Free Inst. Trans., p. 1594.) 
The relation between the Miocene and Pliocene beds of Florida 
will be discussed later. 
Lithologic Character:—Lithologically the two members of the 
Miocene in Florida are very unlike, both in character of the material 
and state of aggregation. The Choctawatchee marl varies from 
greenish gray to light gray in color, and consists of quartz sand con¬ 
taining very large admixtures of shells and shell fragments, and a 
smaller percentage of calcareous sand. In some parts of the formation 
the shells comprise a large percentage of the whole, and they are 
often in an excellent state of preservation. Elsewhere the organic 
remains form a very subordinate part of the whole or they may be 
entirely wanting. One phase of this formation is distinctly plastic, 
and was called “aluminous clay” by Dali and Stanley-Brown . 1 
When examined with a microscope, the marl is found to consist 
of clear quartz sand, of medium fineness, coated and partially ce- 
1 Dali, Wm. H., and Stanley-Brown, Joseph. Cenozoic Geology along the 
Apalachicola River. Bull. Geol. Soc. Amer., vol. v, 1894, p. 157. 
