GEOLOGY: E. BLACKWELDER 
495 
carbonated waters into much thinner beds, in which the proportion of 
P2O5 has arisen to more than 30%. As in the case of guano, more or 
less of the lime phosphate is dissolved along with the lime carbonate, 
and sinking down through subjacent limestones, converts them into 
secondary beds of phosphate rock. Our important Florida deposits 
(the hard rock variety) are believed by Sellards^ to have originated in 
this manner. Other examples of the same type are probably to be found 
in the limestone plateau of southern France, some of the phosphates of 
central Tennessee, and many other regions. 
Phosphatic deposits of any of the types already described may be 
buried to great depths and there be subjected not only to great vertical 
pressures but to the even more intense horizontal strains that accom- 
pany mountain folding. In harmony with the well established principle 
that most rocks tend to recrystallize under these conditions, the phos- 
phatic rocks are probably reorganized. The hydrous minerals char- 
acteristic of the surface must become dehydrated, and there is also a 
tendency for carbonic acid to be driven off. As a result, beds which 
originally consisted of the hydrous carbo-phosphates — collophanite, 
dahllite and others — are believed to pass over into pure apatite, in 
which the proportion of P2O5 may rise to nearly 43% — the maximum 
attainable. Although none of the known apatitic deposits have thus 
far been proved to have originated in this way, it is more than prob- 
able that illustrations of this type exist. It has been suggested that the 
rich apatitic beds associated with the Grenville marbles and gneisses 
near Ottawa, Canada, are really the highly anamorphosed representa- 
tives of phosphatic sediments once deposited on the surface of the land 
or sea bottom. 
There is no obvious reason why deeply buried layers of phosphate 
rock invaded by fluid lava from below should not be dissolved by the 
latter, diffused through its mass, and eventually crystallize as apatite 
disseminated through the resulting igneous rock. Insofar as this occurs 
it closes the cycle, for the phosphorus is thus brought back to its original 
condition, albeit after untold ages of migration and transformation 
in the surficial portion of the earth. 
1 Clarke, F. W., Data of Geochemistry, Bull. V. S. Geol. Survey, No. 616, p. 27 (1916). 
^ According to A. Lacroix, Mineralogie de la France, v. 4, pp. 555 et seq. 
3 Murray, Sir. J., and Philippi, E., Wissensch. Ergeh. der Dcutschen Tiefsee Exped., 
Bd. X, Lf. 4, (1905) (Carl Chun, editor). 
^ Lacroix, A., Mineralogie de la France, v. 4. 
5 Willis, J. L., Ottawa Naturalist, 6, 18 (1892). 
6 Collet, L. W., Proc. R. Soc. Edinburgh 25:, 882. 
7 Sellards, E. H., Florida Geol. Survey, 5th Ann. Kept., pp. 37-66 (1913). 
