52 
FLORIDA STATL GEOLOGICAL SURVEY. 
zone within and presumably at or near the surface of the Vicks¬ 
burg Limestone. This process Eldridge designates as the first period 
during which the primary phosphate was formed. To account for 
the condition in which the rock is now found and for the mixture 
of materials in the matrix Eldridge assumes that at a late period, 
probably at the close of the Pliocene, the peninsula of Florida 
was resubmerged and that during this resubmergence this phos¬ 
phate stratum was broken up, the pieces being removed more or 
less from their original location. To account for the associated 
sands, clays and other materials mixed with the phosphate rock 
he assumes that strong currents were running which washed in 
these complex materials. The phosphate that is now present in a 
finely divided condition and acts as a cementing substance for the 
gray sands was, he assumes, the ground up sediment from the 
hard rock which mixed with the sands as they were drifted into 
their present location. 
The writer’s hypothesis is based on observations by himself 
and others which lead to the conclusion that formations later than 
the Vickburg, formerly extended across the phosphate fields, and 
that these have now largely disintegrated. It is shown also that 
these formations, where now found intact, or as remnants on the 
surrounding uplands, are distinctly phosphatic. From these 
observations it is concluded that the matrix of the hard rock phos¬ 
phate deposits is the residue of the formations that have dis¬ 
integrated in situ, and that the phosphate itself is derived from the 
phosphate originally widely disseminated through these forma¬ 
tions, circulating waters being the agency by which the phosphate 
has been carried to its present location. The gray sands held to¬ 
gether by the finely divided phosphate, referred to by Eldridge, 
are a part of the residue from these earlier formations in which 
the sands occur under similar conditions. 
In the present paper it is not intended to discuss the source of 
the phosphate, which is found widely disseminated in the Upper 
Oligocene and some later formations, from which by solution and 
redeposition it has accumulated to form the workable hard rock 
deposits. The writer does not believe, however, that the bird 
guano theory will account for these widely disseminated phos- 
