50 
FLORIDA STATE GEOLOGICAL SURVEY. 
With regard to the plate rock phosphates of Marion County, 
Johnson (1893) assumes an original deposition of immense beds 
of guano. These beds after the leaching out of their carbonates 
and other soluble materials are believed tO' have become very 
compact, yet not entirely impervious to water. Small cavities in 
close contiguity became finally separated by mere plates and in 
this connection are called laminated rock. By disintegration the 
laminated rock is broken up into fragments, thus giving rise to 
the so-called plate rock. Still further disintegration, in the opinion 
of Johnson, results in the formation of soft phosphate. Johnson’s 
theory as to the origin of the phosphate as expressed in this paper 
is essentially the same as that advanced by Cox in 1890 to account 
for the phosphates as a whole. Johnson’s view that the plate rock 
results from the disintegration of laminated boulders had not 
previously been definitely advanced, although Willis includes a 
statement to this effect in his paper published in 1892. 
Lucius P. Brown (1904) regards it as possible that guano may 
have contributed in a minor degree to the enrichment in phos¬ 
phoric acid of the Florida limestones. The workable deposits of 
phosphate of lime, however, he regards as having been gathered 
up from miscellaneous sources in sedimentary rocks and concen¬ 
trated through the agency of underground water with more or 
less further concentration by mechanical means. 
Mr. P. Jumeau (1905) reviews the theories proposed to 
account for the origin of the phosphate rock, pp. 68-82. That the 
phosphate rock has accumulated chiefly from the leaching of 
guano is regarded by him as the most probable theory. 
DISCUSSION OF THEORIES. 
The theories offered by Wyatt, 1890, and by Pratt, 1892, are 
highly speculative and are based on assumptions for which nc 
proof is offered. Of this class also are some other theories that 
have appeared from time to time in newspaper and magazine 
articles. 
Davidson assumes that the phosphate rock existed originally 
in the Vicksburg Limestone and in its present form is merely 
