EEPOKT ON" THE PHOSPHATE FIELDS OF SOUTH CAROLINA. 7 
drain into this ditch from the phosphate trenches, which are thus kept 
comparatively dry. A main line of railroad is established, and spurs 
from this are run out to the phosphate trenches in such a way that 
the material can be loaded easily into flat cars and hauled cheaply to 
the washer plant. 
Hand mining is usually performed on contract, a certain price being 
paid for the rock delivered at the washer. The contractor in turn 
pays the laborers by the task, assigning each man a section of the 
phosphate property, from which he removes the overburden and digs 
out the phosphate and loads it on the cars. Where the overburden is 
8 feet or more in thickness steam shovels are employed to remove it. 
This machine digs a canal about 20 feet wide, depositing the over- 
burden on one bank, while a hoist equipped with a single grab bucket, 
or a series of buckets to be loaded by hand, runs on a track on the 
opposite bank of the canal. As fast as the steam shovel removes 
the overburden from the deposit the hoist is used to place the phos- 
phate thus exposed on the cars. When the limit of the deposit is 
reached the steam shovel returns, dredging out a canal adjacent to 
that already dug and depositing the overburden in the old ditch. 
Many deposits which could not be economically worked by hand are 
now rendered valuable by the advent of machine mining. (PL II, 
figs. 1 and 2.) 
WASHING THE ROCK. 
After the washing of the material by hand had been abandoned as 
entirely inadequate and inefficient, log washers similar to those now 
used in Florida 1 were introduced. The matrix in which the South 
Carolina phosphate is embedded, however, is of such a loose char- 
acter that an elaborate cleansing process is unnecessary, so that log 
washers have been supplanted. By the present method the rock is 
scraped into a hopper, which discharges into a mechanical conveyor 
composed of units holding one-half ton each. It is carried to the top 
of the washer, where each unit of the conveyor is automatically dis- 
charged, and a stream of water washes its contents down to a crusher. 
From the crusher it is discharged through troughs into the lower end 
of several cylinder washers, which vary in number from two to 
eight, depending upon the size of the plant. Each cylinder is 27 feet 
long and 5 feet in diameter, the discharge end being 14 inches higher 
than the end where the phosphate material enters. The first part of 
the lower end and the last 2 feet of the upper end are composed of 
heavy wire screen, having perforations of a dimension three-sixteenths 
by three-fourths inch. 
The interior of the cylinders is fitted with plates arranged in the 
form of a spiral so that they throw the phosphate forward and toward 
1 Waggaman, Bui. No. 76, Bureau of Soils, U. S. Dept. Agr. (1910). 
