8 BULLETIN 18, U. S. DEPARTMENT OF AGRICULTURE. 
the upper end as the cylinder revolves. A 2-inch stream of water 
under a pressure of 60 pounds to the square inch is played upon the 
phosphate material from the upper end of the cylinder. This 
washes the sand, clay, and finely divided phosphate down to the lower 
end of the cylinder where it escapes through the screen and then flows 
out through a trough to the wash heap, which is usually located at 
some distance from the plant. The washed rock falls from the upper 
end of the cylinder upon a rubber-coated belt 26 to 30 inches in width, 
along which it is carried to the wet bins. Pickers are stationed along 
this belt for the purpose of removing clay balls, marl, and any other 
foreign material which may be mixed with the phosphate. From 
the wet bins the rock is drawn into cars and sent to the drying sheds, 
where it is burned on ricks of wood. About 6 cords of wood are re- 
quired to dry 100 tons of phosphate from a moisture content of 15 per 
cent down to a moisture content of 0.5 per cent. 
COST OF PRODUCTION. 
Unfortunately for the South Carolina phosphate industry, the cost 
of production has increased without a corresponding advance in the 
price of phosphate rock. Indeed, the price of this material is now so 
low that the smaller operators in these fields have entirely ceased 
mining. 
The increased cost of mining is largely due to the practical exhaus- 
tion of the more accessible deposits. It is now frequently necessary 
to remove an overburden of 15 to 20 feet in order to uncover the 
phosphate stratum, where formerly there were hundreds of acres of 
rock lying practically at the surface or covered by only a foot or two 
of soil. 
The price of labor has also advanced from 30 to 50 per cent, and 
frequently it is so difficult to obtain hands that the output of rock 
is seriously curtailed. The equipment of a modern phosphate plant 
is both elaborate and costly. Steam shovels for excavation, grab 
buckets and hoists for taking out the rock, many miles of steel rails, 
locomotives and flat cars for haulage purposes, heavy machinery for 
washing the rock, and large sheds for drying and storing the product 
are essential parts of the present mining system. (PI. Ill, figs. 1 
and 2.) 
On account of the topography of the South Carolina coast, weather 
and tide conditions affect the output of phosphate rock. In rainy 
weather or when the tide is very high the trenches are continually 
filling with water, the banks caving in, and the continual use of 
pumps is necessary to make mining possible. The output of rock 
under such conditions is often cut in half, thus practically doubling 
the cost of mining per ton. 
