y6 FLORIDA GEOLOGICAL SURVEY-SEVENTH ANNUAL REPORT. 
THE RIVER PEBBLE PHOSPHATE DEPOSITS. 
The river pebble phosphates are found in Florida in varying 
amounts wherever streams have cut their channels into the phos- 
phatic marls either of the Alum Bluff or of the Jacksonville forma¬ 
tion, or across the phosphate conglomerate of the Bone Valley for¬ 
mation. The pebbles may be found in recent bars in the streams, or 
in the bars of an earlier channel or valley. The age of the deposits, 
therefore, on any one stream, may range from Pleistocene or earlier 
to recent. The immediate origin of these local river deposits is 
obviously the formation across which the stream flows. In' grade 
the river pebble deposits seldom exceed 66% tri-calcium phosphate. 
FOSSILS FROM THE RIVER PEBBLE PHOSPHATE DEPOSITS. 
The vertebrate fauna of the river pebble phosphate deposits of 
Florida includes elephants, mastodons, horses of the genus Equus, 
bison, deer, tapir, manatee, sloths, glyptodonts, and armadillos. 
With this assemblage of clearly Pleistocene forms is associated in 
some localities probably by accident the Pliocene horse Hipparion. 
The deposits contain also cetaceans, turtles, crocodiles and fishes. 
Elephants were present in Florida during the Pleistocene and 
possibly during a part of the late Pliocene, their remains being 
found at many localities throughout the State in the river pebble 
phosphate deposits and elsewhere. The Florida elephant has usually 
been identified as Elephas columbi Falconer. It would seem, how¬ 
ever, that the enamel folds or plates in the teeth are coarser and far¬ 
ther apart than are those of E. columbi . According to Lucas* 
the number of cross folds in the teeth of E. columbi average eighteen 
in a space of ten inches, while in the teeth of the Imperial elephant 
the cross folds average twelve in the same space. The number of 
cross folds or plates in the elephant teeth that have been obtained by 
the writer from Florida will seldom exceed twelve to fourteen in a 
space of ten inches. 
The mastodon commonly found in the river pebble phosphate 
deposits is that known as the American mastodon, Mammut ameri- 
canum, a species that extended during Pleistocene time over a con¬ 
siderable part of North America. This mastodon is distinguished 
from those found in the land pebble phosphate deposits by the fact 
*Md. Geol. Surv. Volume on Pliocene and Pleistocene, p. 159, I9°6- 
