ORIGIN OF THE HARD ROCK PHOSPHATES. 
45 
1891) ,E. T. Cox ( 1890, 1891, 1892, 1896), Walter B. M. David¬ 
son (1891, 1893), N. A. Pratt (1892), C. C. Hoyer Millar (1891, 
1892) , G. M. Wells (1896), E. W. Coddington (1896), L. P. 
Jumeau (1905, 1906). 
THEORIES PREVIOUSLY PROPOSED. 
The hard rock phosphates of Florida have interested all 
who have examined them, and many theories have been advanced 
to account for these remarkable deposits. In the following review 
these various theories are given as nearly as practicable in the 
order in which they are proposed. A strictly chronological order 
is, however, often impossible since when several papers appear 
during the same year it is difficult to determine which was first 
issued. Moreover some of the papers were evidently written 
some years before being printed. 
The paper by Dr. Albert R. Ledoux read before the meeting 
of the New York Academy of Science, January 27, 1890, and 
published in the transactions for 1890 is apparently the first 
account of the hard rock phosphate deposits that has been 
preserved. In this paper Dr. Ledoux offers no specific theory for 
the Florida deposits. Speaking of phosphates in general, how¬ 
ever, he notes the fact that within the rain belt, when guano 
deposits rest upon limestone the phosphoric acid is leached out 
and alters the carbonate of lime to phosphate. An instance is 
cited in this connection in which limestone in one of the South 
Pacific islands was believed to have been changed to phosphate to 
a depth of several feet within the period of twenty years. The 
phosphoric acid in this instance was leached by rainwater from 
recently deposited guano. The suggestion of the replacement of 
the carbonate of limestones under certain favorable conditions by 
phosphate is not offered by Ledoux as a new hypothesis, as this 
method of formation of certain of the phosphates had been dis¬ 
cussed by various previous writers. 
In a paper published in the New York Mining and Engineer¬ 
ing Journal for August 23, 1890, Francis Wyatt proposed the 
theory that the hard rock phosphates are due to the evaporation 
