$40 Florida state: geological survey 
Section at the sink three miles southeast of Brooker. 
13. Covered and sloping . 14 feet. 
12. Cream or light colored marl full of small shells.. feet 
11. Yellowish sand matrix holding black pebble phosphate. 5 feet. 
10. Sandy limestone ledgq with fossils."... ^ foot. 
9. Yellow sand matrix with fossil plants and pebble phosphate.... 4 feet. 
8. Concretionary limestone ledge ..... 2% feet. 
7. Steel gray colored sand-clay oxidizing yellow. 5 feet. 
6. Concretionary ledge containing pebble phosphate.. 1 foot. 
5. Sandy matrix with pebble phosphate. 4 feet. 
4. Concretionary ledge .. 5 feet. . 
3. Clayey matrix holding black pebble phosphate.. 5 feet. 
2. Concretionary ledge ..... V/ 2 feet. 
1. Clayey matrix holding black pebble phosphate. 4 feet. 
Total depth to the water’s edge .... 75 feet. 
The sink at which this section is made is circular in outline and 
is possibly 200 feet across. The depth of the sink to water level is 75 
feet; the depth below water level has not been determined, although it 
is reported to be more than 100 feet. With the exception of the en¬ 
trance of a small stream from the east the sides are almost perpendic¬ 
ular. This stream has cut its channel through to the hard ledge of 
stratum No. 4, over which it forms a waterfall. Strata numbers one 
to four of the section stand vertical entirely around the sink. The 
sands of numbers five to eight weather brownish in color, forming a 
conspicuous band surrounding the sink, except where cut across by 
the stream. The sands of number nine and eleven slope slightly from 
the lack of supporting ledges. The marl, number twelve, stands ver¬ 
tical or nearly so. 
From its considerable thickness the phosphate pebble bearing for¬ 
mation of this section may be expected to be found underlying a con¬ 
siderable area in this part of the State. The pebble phosphate in this 
exposure is of a brownish color differing from the land pebble phos¬ 
phate of south Florida and resembling in this respect the river pebble. 
This formation is without doubt the matrix from which have been 
washed the phosphates of Black Creek and other tributaries entering 
the St. Johns River. 
LOSS OF PHOSPHATE IN MINING. 
That there is considerable loss of phosphate in mining is well 
known. Practically all deposits contain along with other material 
more or less phosphate in a soft or pulverulent condition. Under 
present methods of treatment this “soft” phosphate is necessarily lost 
in the process of washing, being carried to the dump along with the 
