48 
FLORIDA STATE GEOLOGICAL SURVEY. 
stone. He says, page 12, “The phosphates of Florida, in all 
shapes, I derive from the leaching of the Vicksburg limestone, and 
in the same way I would account for the phosphates of the West 
India Islands. The phosphatic limestone of these islands has been 
subject to the leaching action of rains and atmosphere reactions, 
and the carbonate of lime has been carried away, leaving on the 
surface the more insoluble phosphate, and the iron and alumina. 
As in all limestones, the water eats away the rock unevenly, mak¬ 
ing pits and holes, and caves, and the phosphate of lime fills them 
up—either in an earthy form, or in the massive variety, which is 
described as coating the stalagmites and stalactities in the cave 
in Navassa.” Davidson believed that after the phosphate had 
accumulated in the pits and holes in the limestone, Florida was 
again submerged, allowing the sea sand to accumulate over and 
around the boulders. 
Pratt (1892) while conceding that the theory of a pure bird 
deposit, in localities favorable to the roosting of water fowl, more 
nearly covers the conditions of the problem as presented in all 
localities than any other so far advanced, considers that in the case 
of the Withlacoochee River deposits the evidence is all opposed to 
this theory. In this paper the theory is advanced by Pratt that the 
phosphate boulder is a true fossil, the boulder being the phosphatic 
skeleton of a gigantic foraminifera, while the soft phosphate is 
supposed to be the germ spores or bud of the animals or the com¬ 
minuted debris of the animals themselves.* 
Millar (1892) reviews the theories current at that time (pp. 
115-117) and favors the view that guano is the most probable 
source of the phosphate. 
Whether the hard rock phosphates of Florida resulted from a 
superficial and heavy deposit of soluble guano, or from the con¬ 
centration of phosphate of lime already widely and uniformly dis¬ 
tributed throughout the mass of the original rock, or from both 
*The original of Dr. Pratt’s paper not being accessible to the writer 
thio review is based on the quotation from the paper included in the Phos¬ 
phate Industry of the United States by Carroll D. Wright, 1893, pp. 24-31, 
and in the Florida, South Carolina, and Canadian Phosphates by Millar, 
1892, pp. 73-77 and 117. 
