38 
FLORIDA STATE GEOLOGICAL SURVEY. 
the reworking and reaccumulation of the materials. The phos¬ 
phate and flint boulders are formed chemically through the agency 
of ground water. The formation containing the hard rock phos¬ 
phate is limited in its distribution to that section of the State in 
which formations carrying more or less phosphate have disinte¬ 
grated, overlying a limestone substratum, thus affording condi¬ 
tions favorable for the downward passage of rain water carrying 
phosphoric acid in solution. The phosphate thus removed from 
the surface formations is reaccumulated under these conditions in 
a concentrated form at a lower level. The phosphate deposits 
are localized within the formation because the formation itself is 
lacking in uniformity. Local variations, particularly the presence 
of clay lenses and other conditions which interfere with the free 
circulation of ground waters, favor the formation of phosphate 
boulders and thus result in a local deposit of phosphate rock of 
sufficient amount and purity to be of commercial value. The plate 
rock represents chiefly fragments of disintegrated boulders. 
ACKNOWLEDGMENTS. 
In presenting this view of the origin of the hard rock phos¬ 
phates the writer takes pleasure in acknowledging his indebted¬ 
ness to the many investigators who have contributed to a knowl¬ 
edge of these deposits. This indebtedness is not alone to those 
who have written on the origin of the phosphates, but equally 
to those who have contributed to an understanding of the geology 
of the State as a whole, and particularly of that part of the State 
in which these deposits are found. Only a few of these general 
publications can be mentioned at this time, although a full list is 
included in the bibliography which forms a part of the First 
Annual Report, of the State Geological Survey, 1908. 
The monograph on the Tertiary Fauna of Florida by Dr. W. 
H. Dali published in the Transactions of the Wagner Free Insti¬ 
tute of Science, 1890 to 1903, includes by far the most extensive 
study of the invertebrate fauna of the Florida formations that 
has yet been made, and to these investigations we are indebted 
for many fundamental facts regarding the succession of forma- 
