60 FLORIDA GEOLOGICAL SURVEY—SEVENTH ANNUAL REPORT. 
A conglomerate partakes of the characteristics of the rock from 
which, it is derived. In regions where the country rock is resistant, 
and especially where it is shattered by the action of frost, the resid¬ 
ual material on the hillsides and in the stream beds is likely to 
contain a large proportion of coarse rock fragments. The rock 
from which the conglomerate of the pebble phosphate beds was de¬ 
rived, however, is for the most part a rather soft marl with a vary¬ 
ing amount of sand, clay and phosphate pebble. The residual ma¬ 
terial that accumulates when a rock of this character is submitted 
to a sub-areal erosion consists, as may be seen in sections where this 
formation is now the country rock, chiefly of sand and clay, there 
being only a limited amount of phosphate pebble in the sub-soil. 
Under these conditions it is not surprising to And that the materials 
first .accumulated in the depressions contain frequently a considerable 
proportion of sand and clay, while that which follows may include 
a larger amount of phosphate pebble and rock fragments washed 
or broken by the waves or streams from the bed rock. However, 
as each depression is differently located with regard to the sweep of 
waves and the force of the currents, endless variations in the de¬ 
posits accumulated must be expected. When the sea but partly 
covers the land and is shallow, obviously the force of the waves is 
slight. If depression continues until a larger part of the land is 
submerged, the waves gain a greater sweep. With progressing 
submergence, there comes a point of maximum effectiveness of wave 
action in washing* and moving materials. Finally, however, the 
shore line is removed to such a distance that the phosphate pebble 
are no longer carried in quantities sufficient to make up workable 
beds. In other words the phosphate beds then give place to the 
phosphatic sands of the overburden. 
Moreover, it is quite possible that the submergence of the land 
area was attended by minor oscillations in level. It is not improbable 
for instance, that following partial submergence and the accumula¬ 
tion of deposits near the shore line, the land area may have been 
slightly elevated. If so, the shore line was changed, and the streams 
of the adjacent land area rejuvenated. The phosphate deposits that 
had accumulated near the former shore line were then reworked, 
the finer materials removed, and the coarse rock reaccumulated in 
shallow water near the shore, the deposits resulting from this second 
concentration being more thoroughly washed and richer in pebble 
phosphate than were the beds first deposited. It seems quite pos- 
