6 BULLETIN 18, U. S. DEPARTMENT OF AGRICULTURE. 
After calcining, the rock becomes more brittle and can be readily and 
cheaply ground. 
Although the South Carolina phosphate is considerably lower in 
grade than that from many other sources, it makes an acid phosphate 
of excellent quality and good mechanical condition for mixing pur- 
poses. Some farmers prefer this material to the higher grade prod- 
uct made from Florida or Tennessee phosphate. 
The rock now marketed contains on the average about 61 per cent 
of bone phosphate of lime, though individual nodules and fragments 
are sometimes found which contain as much as 75 per cent. The 
following table, compiled by Chazal from analyses made by Shepard, 
gives the composition of South Carolina phosphate from different 
localities. The samples from which these analyses were made were 
collected during the early development of the South Carolina phos- 
phate industry and are of somewhat lower grade than the rock which 
is now obtained from some of the same localities. 
Table II.— Phosphate content of South Carolina phosphate rock from various sources. 
Location. 
Description. 
Moisture. 
P 2 5 , 
undried 
basis. 
Ca 3 (P0 4 ) 2 , 
undried 
basis. 
Ca 3 (P04) 2 , 
dried 
basis. 
Per cent. 
3.68 
Per cent. 
25.61 
20.68 
25.70 
27.01 
27.11 
27.26 
25.14 
27.26 
26.78 
Per cent. 
55. 91 
58.24 
56.21 
58.95 
59.18 
59.51 
54.88 
59.51 
58.46 
Per cent. 
58.04 
Do . 
Do .. 
1.50 
.00 
10.07 
.84 
.79 
.57 
.66 
57.07 
Ashley River, land deposit 
Hot air-dried cargo sample. . 
58.95 
Hot air-dried cargo sample. . 
.. .do. . . 
60.00 
Bull River 
55.32 
...do... 
59.85 
Do 
...do... 
58.85 
METHODS OF MINING. 
For many years the mining of South Carolina phosphate was car- 
ried on by hand labor. For a short time even the washing of the 
phosphate was done by hand. The product, therefore, was at first 
regarded rather unfavorably, as it was not clean and produced an acid 
phosphate of poor quality. The early methods of mining and hand- 
ling the rock have been largely supplanted by modern and more 
efficient methods, which turn out a clean, dry product well fitted for 
the manufacture of acid phosphate. Hand mining is still economi- 
cally practiced where the overburden is sufficiently light and of such 
a character as to render the steam shovel unnecessary, but washing 
by hand has been entirely supplanted by the modern washer plant 
capable of turning out from 150 to 600 tons of clean rock every day. 
Hand mining (see PI. I, figs. 1 and 2) is carried out as follows: 
After thorough prospecting to determine the extent and value of the 
phosphate property, a ditch is dug through or alongside the tract to 
be mined and below the level of the phosphate stratum. Laterals 
