138 
FLORIDA STATE: GEOLOGICAL SURVEY. 
A few of the other described species do not throw any light on the question 
of age. Those marked with an asterisk are not yet shown to be distinct from the 
corresponding species of the other horizons. It thus appears that six species 
are allied to or identical with as many of the Loup Fork horizon of the West, 
while four are characteristic of the Equus beds of the East, of Texas, and of 
South America. The epoch they represent is then probably between the two. 
BONE VALLEY GRAVEL. 
The deposits here called Bone Valley gravel have been described 
by both Eldridge 1 and Dali . 2 They comprise nearly all of the pebble 
phosphates now being mined in Florida, and the name is derived from 
a locality west of Bartow, where the beds are exploited on a large 
scale. The names formerly used for this formation varied somewhat 
with different writers. Eldridge designated the deposit as land pebble 
phosphate, while Dali called them simply pebble phosphates. Both 
writers distinguished between the Tertiary deposits of Pliocene age 
and the younger pebble phosphate which vary in age from Pleistocene 
to Recent. 
That these beds were regarded by Dali as Pliocene will be seen 
from the following quotation : 3 
A very large area in central and southern Florida was probably covered by 
this older marine Pliocene. There appear to be traces of it at Clay Landing and 
other points on the lower Suwanee River, and it is not unlikely that the whole 
great Suwanee swamp region may be underlain by it, as well as the DeSoto 
lake area. There are traces of it in the rocks of the upper Alefia, but farther 
to the west and north, on the Hillsboro,so far as known, if any of this rock was 
deposited, it has since been removed. I incline to the belief, however, that the 
Hillsboro region, from its relation to the great western anticline was not de¬ 
pressed below the sea during this part of the Pliocene. The “pebble phosphates" 
of the upper Alefia, like those of the Peace Creek basin, are, as far as yet 
observed, entirely of this rock, and on the Alefia researches hitherto made have 
failed to find the subsequent marine Caloosahatchee Pliocene represented. 
There are both physiographic and lithologic reasons for thinking 
that these gravels are in considerable measure of fluviatile origin. They 
are situated in the valleys of streams and vary in altitude from less 
than twenty-five feet to nearly a hundred feet above tide. Lithologi¬ 
cally, the formation is composed of very poorly assorted materials, such 
as clay and phosphate pebbles, which usually show some evidence 
of stratification. If the gravel beds were deposited during gradual sub- 
1 Eldridge, Geo. H., Preliminary sketch of the phosphates of Florida, Am. 
Inst. Mng. Engrs., vol. xxi, 1893, pp. 196-231. 
2 Dali, Wm. H., Neocene of North America, U. S. Geol. Survey, Bull. 84, 
•1892, pp. 137-138. 
3 Dali, Wm. H., Neocene of North America, U. S. Geol. Survey, Bull. 84, 
1892, pp. 141-142. 
