ORIGIN OR THR HARD ROCK PHOSPHATES. 
57 
become incorporated in the phosphate deposits. Among the 
residual fossils are sharks’ teeth, which are obtained in numbers 
from every pit that is operated. It is frequently stated by the 
miners that the sharks’ teeth become more abundant as the under¬ 
lying limestone is approached near the base of the deposits. This 
statement is consistent with the view that many of the teeth are 
residual from the underlying limestone. The less resistant parts 
of the skeleton can not be expected to have persisted from these 
early formations in such abundance and such perfect state of pres¬ 
ervation as have the teeth. 
The residual fossils are of value to the geologist since from 
them it may be possible to determine from what particular forma¬ 
tions the materials of the matrix have been derived. The fossils 
included with the phosphate, not residual, indicate the age or time 
during which the reworking of the materials occurred. 
The fossils that were incorporated with the materials while 
they were being, reworked and redeposited are, as would be 
expected, of much later date than the residual fossils. Of these 
later animals comparatively fragile bones are frequently preserved. 
Whole skeletons, however, are rarely found in place. This may 
be due to the conditions under which they .were entombed, or 
possibly to the fact that the parts of the skeleton have been 
subsequently more or less dissociated by the subsidence of the 
materials due to the solution of the underlying limestone. 
From the fact that the formation of caves and sink holes in the 
limestone has continued to the present time it is evident that some 
comparatively recent fossils are likely to become included with 
the phosphate. Moreover local fresh water Pleistocene or recent 
surface deposits are likely to occur as a part of the overburden 
from which fossils may become mixed with the phosphate. Along 
the Withlacoochee River, which cuts through these deposits, also 
there has doubtless beep more or less shifting of the stream by 
which Pleistocene and recent remains are included with the phos¬ 
phate. These are conditions that must be borne in mind in making 
and in studying the collections. 
Of the fossils that are accepted as contemporaneous with the 
phosphate formation the best authenticated is a species of 
