PEBBLE PHOSPHATE DEPOSITS. 
67 
formation. The accumulation of this amount of clay with little 
coarse pebble may be readily understood. Doubtless this particular 
depression was so located that when the area was partially sub¬ 
merged it did not receive the strong wash of either waves or stream 
currents, but received only the clay or mud from the wash of the sur¬ 
rounding lands. These conditions continued until some 12 or 15 
feet of mud with little coarse material accumulated at this spot. 
Afterwards, however, the conditions changed somewhat so that a 
conglomerate of pebble accumulated of sufficient thickness to form 
the workable beds of the pit. Similar conditions may be expected at 
other localities. 
SAND AND FINE PEBBLE BENEATH THE PEBBLE PHOSPHATE 
CONGLOMERATE. 
In one of the pits of the Pierce Phosphate Company that was 
being worked some years ago>, there were to be observed lying be¬ 
neath the workable phosphate beds, one to three feet of quartz sand 
intimately mixed with black phosphate pebble. A deposit of this 
kind lying near the bed rock is not uncommon, and by the miners 
is called “pepper and salt.” As in the case of the clay beds the 
“pepper and salt” is evidently the result of local conditions. The 
material in this particular case was fairly well sorted, the sand 
grains and the minute phosphate pebble being of approximately the 
same weight. 
IRON ROCK IN THE OVERBURDEN 
Occasionally the overburden, or several feet of it next beneath 
the soil, becomes firmly cemented. Under these conditions the rock 
may become very hard necessitating blasting. The cementing sub¬ 
stance in most instances is iron oxide, carried into the sand by sur¬ 
face water. This phase of the overburden was observed in the pit 
of the Florida Mining Company near Mulberry, where the section 
was as follows: 
it Incoherent sand and soil-• 6 feet 
2. Indurated sands, reddish in color and probably cemented with iron 
oxide ---10 feet 
3. Phosphate bed---15 feet 
4. Yellow marl, “bed rock.” 
