ORIGIN OR THE HARD ROCK PHOSPHATES. 
59 
entire extent from the Apalachicola River, in West Florida, through 
Northern and Central Florida. The red sandy clays forming the 
surface deposits over much of Northern Florida and which prob¬ 
ably extended across the phosphate section overlying the 
Oligocene deposits, contained fragments from the granitic rocks 
and have doubtless contributed in the process of decay more or 
less phosphoric acid. 
AGENCY. 
The agency by means of which the phosphates were accumu¬ 
lated in their present form was ground water. The rainfall, which 
in Florida amounts to about 54 inches per annum, in passing 
through the surface materials dissolves a limited amount of the 
phosphate, which is carried to a lower level and is finally thrown 
out of solution in a. concentrated form. This process long 
continued results in the accumulation of workable phosphate 
deposits. 
RELATION-TO THE UNDERGROUND WATER LEVEL. 
It is probable that the ground water level has had an impor¬ 
tant bearing on the formation of the phosphate deposits. There 
is, as is well known, a definite relation between the ground water 
level and chemical reactions within the earth. The conditions 
above and below this level are radically different. Above the 
ground water level the movement of water following rains is free 
and solution is active; below this level the water stands or has a 
scarcely appreciable movement. Above the water level solu¬ 
tion is active, while below this level deposition frequently occurs. 
It is important to observe in this connection that the under¬ 
ground water level, in Central Florida, which has such a direct 
bearing on chemical deposition has not always remained the same. 
In former times when the surface stood at a higher level the water 
table was higher above sea than at present. In other words, a 
lowering of the general surface level by erosion was accompanied 
by a lowering of the water table. It thus happens that a locality 
which in one stage of physiographic development is favorable to 
the formation of phosphate rock, may in a subsequent stage, when 
