58 
FLORIDA STAFF GEOLOGICAL SURVFY. 
composed of Orbitoides mantelli. The rock, where it is quarried at 
this locality, appears to form a well defined ridge covered by a few 
feet of white Pleistocene sand and sandy loam, but its presence is 
indicated at various points by numerous boulders containing char¬ 
acteristic organic remains. 
A few miles northeast of Duncan at Falling Water, a large sink 
exposes several feet of light gray limestone, probably belonging to 
the same formation. At this locality there appears to be a well de¬ 
fined system of underground drainage, which is indicated at the sur¬ 
face by numerous sink-holes. The best exposure is seen where a 
small stream plunges into one of these sink-holes. The stream is 
reported to have a fall of over seventy feet. The rock here forms a 
nearly perpendicular cliff and hence the section is not easily accessible. 
At Natural Bridge near the north line of Walton County, a light- 
gray to vellowish-gray marl forms the arch which spans a small 
stream. The width of the channel is probably twenty feet and the 
length of the bridge about one-fifth of a mile. The height of the 
exposure was estimated by Vaughan 1 to be about thirty-five to forty 
feet above the level of the water in the creek. When fresh, this rock 
is soft and crumbles readily in the fingers, but when exposed to the 
weather it hardens rapidly and assumes the yellowish color mentioned 
above. It is quarried by sawing and is locally known as chimney rock, 
because it is used in the construction of chimneys. A considerable 
percentage of clay, which occurs in fine particles distributed through 
the rock, indicates that the material is a marl rather than a limestone. 
Pecten poulsoni is the most abundant fossil. From the lithologic 
character of the rock, together with the occurrence of numerous speci¬ 
mens of the species mentioned above, the rock is considered to belong 
to the Marianna limestone. 
A quarter of a mile south of the Bridge near a turpentine still a 
similar marl is exposed in the bed of a small stream. The outcrop at 
this locality has a thickness of about twenty feet and it differs lith¬ 
ologically from the marl of the Bridge in being slightly more compact 
and of a distinctly grayish or bluish color. However, these differences 
are probably due to the fact that this exposure has not suffered so 
much weathering as the one at the Natural Bridge, and the sub¬ 
stantial equivalence of the rock at the two localities can hardly be 
questioned. Numerous concretions of nearly pure carbonate of lime 
are scattered throughout this marl, but they do not appear to have 
any relation to the occurrence of the fossils. 
About seven miles southwest of Marianna and nearly one mile 
from Kynesville, a number of fragments of limestone were obtained 
1 Vaughan, T. Wayland, unpublished notes. 
