tenroseI PHOSPHATES OF SOUTH CAROLINA. 69 
erhood dredge. It consists of a revolving chain of thirty-two buckets, 
and is very similar to the dredge used to deepen the channel of the 
St. Lawrence River some years ago. 
The deposits of South Carolina, though of low grade compared with 
some others, are now more generally used than any other known phos- 
phato. The output of the mines, which is yearly increasing, is shipped 
to the North, South, and East by sea and to the West by rail. This 
popularity is due, not only to the cheapness of the phosphate ($') to $6 
per ton in 1886), but to the many good qualities "of the low-grade acid 
phosphate made from it. The fact that the nodule bed extends, at an 
accessible depth, over many miles of country, the easy approach for large 
vessels up to the very mines, the abundance of water, fuel, and labor, and 
a climate that permits mining operations to be carried on throughout 
the whole year, all combine to make the South Carolina phosphates the 
cheapest and consequently the most productive source of supply of 
this material. 
The mode of formation of the South Carolina nodules has been a mat- ' 
ter of considerable dispute. Professor Holmes thinks that the surface 
of the Eocene marl was worn, by the action of boring animals and of 
erosion, into numerous lumps and balls. These, with bones of sea ani- 
mals, were washed upon the seashore and, as the coastline began to rise, 
were collected into salt-water lagoons and swamps. Numerous quad- 
rupeds came to lick the salt, and deposited their faeces and often died 
here. Hence the presence of bones of laud and sea animals in the phos- 
phate beds. The phosphoric acid in the fseces and carcasses of these 
animals phosphatized the lumps of marl and thus formed the phosphatic 
nodules. 
Prof. N. S. Shaler thinks that the nodules, in sonie cases, have been 
formed by concretionary and segregating action at the bottom of 
swamps. Many facts, such as the frequent occurrence of phosphatic 
nodules in patches, and often in concave basins, as in Russia, as well 
as their association with peaty beds, as in North Carolina, seem, in 
many cases, to strongly favor this theory. Phosphatic nodules have 
also been found at the bottom of beds of limonite in the Ohio Valley. 
Professor Shaler thinks that the nodules were scattered sparingly in 
the deposit in which they were formed and that they were concentrated 
in their present position by the erosion of the original bed. 1 
^Analyses of South Carolina rock phosphates, by Dr. C. TJ. Shepard, jr., in South Carolina 
Phosphates, Charleston, 1880. 
An average of several hundred analyses gave : 
Per cent. 
Phosphoric acid 25 to 28 
Equi valent to bone phosphate of lime 55 to 61 
iCarbonic acid 2. 5 to 5 
Equivalent to carbonate of lime 5 to 11 
1 Proc. Boston Soc. Nat. Hist., vol. 13, 1809-70, p. 222. 
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