28 
FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
irregular. In general clay lenses in the phosphate matrix are most 
frequent in the upper part of the formation. 
The red clayey sand called “hardpan” by the miners may be 
present or lacking in the pits of this section. The loose pale yel¬ 
low sand is practically always present varying in thickness from 
i to 25 feet. 
MARION COUNTY. 
The plate rock deposit found in the vicinity of Anthony and 
Sparr in the north central part of Marion County represents an 
eastward extension of the phosphate-bearing formation. The 
relation of the phosphate matrix to the underlying limestone is the 
same as previously described. The limestone projects into the 
phosphate matrix as rounded peaks. (PI. 5.) Circular depres¬ 
sions similar in appearance to pot holes or to “natural wells” are 
frequent in this section. These through subsidence are filled with 
the phosphate matrix. One of these depressions observed by the 
writer had been cut into, in the process of mining. This depres¬ 
sion was about three and one-half feet in diameter at the top. 
fifteen feet deep and narrowed gradually to the bottom. Other 
depressions, variable in diameter and in depth occur. The lime¬ 
stone lying below the line of the underground water level has us¬ 
ually a rough and jagged surface owing to solution by water in 
contact with the limestone. Above the water level the limestone 
has a sihooth rounded surface. The shells and other fossils below 
water level are often removed by solution; above this level they 
are eroded off plane with the general rock surface. The plate 
rock beds show evidence of having been originally faintly strat¬ 
ified. Much of the stratification that originally existed, however, 
has been destroyed through repeated local subsidence as the un¬ 
derlying limestone was removed by solution. The stratification 
lines in the plate rock are frequently much curved and distorted ow¬ 
ing to this irregular subsidence. (PI. 2, Fig. 3.) 
The chief difference noted between the plate rock and the ty¬ 
pical hard rock region is in the relatively large amount of fragmen¬ 
tary phosphate rock and small amount of boulder rock. In other 
words the mechanically transported rock in this section predom¬ 
inates over the rock formed chemically in situ. Flint and lime¬ 
stone boulders chemically formed are likewise absent or rare. 
The deposits at Standard and at Juliette in the western part of 
Marion County are similar in general character to the hard rock 
deposits as previously described. The mines in this section are 
