62 
FLORIDA STATE GEOLOGICAL SURVEY. 
SECONDARY DEPOSITION OF PHOSPHATE FROM 
SOLUTION. 
■ In many boulders a secondary deposition from solution may 
be recognized. Practically all the laminated boulders show a 
rough mamilated or stalactitic undersurface of each lamina, while 
the top surface of the lamina next beneath show successive layers, 
separated by minute parting planes, indicating successive deposi¬ 
tion of phosphate from solution. This process is similar to that 
which takes place in caves where calcium carbonate is deposited 
to form stalactites and stalagmites, and is probably confined to 
boulders lying above the permanent ground water level. Many 
small pieces of rock were doubtless phosphatized without having 
assumed the boulder form. 
ORIGIN OF THE PLATE ROCK. 
The plate rock deposits represent a peculiar phase of the hard 
rock formation. It seems probable that the plate rock represents, 
in part at least, fragments of boulders that have disintegrated, as 
was suggested by Johnson in 1893. It has also been suggested 
that these plates may have been formed by finely' divided phos¬ 
phate mud settling as a sediment. 
As previously stated many of the boulders have a laminated 
structure. When such boulders disintegrate the laminae break 
up, giving rise to the flattened pieces to which the term plate 
rock is applied. In this connection it is interesting to observe 
that the plate rock occurs in those sections of the field in which 
the phosphate deposits now lie above the water level, and have 
been subjected to disintegrating influences. The plate rock 
deposits, as at Anthony and Sparr, form a comparatively thin cov¬ 
ering over the Vicksburg Limestone and represent, in the writer’s 
interpretation, the disintegrated remnant of an ordinary hard rock 
phosphate deposit. 
The gravel found mixed with the hard rock very possibly 
represents in part small bits of rock that have become phos¬ 
phatized and in part fragments of larger rocks. The soft phos¬ 
phate associated with the hard rock has very generally been 
