G2 DEPOSITS OF PHOSPHATE OF LIME. [bull. 46. 
or, better, when two fragments are rubbed together, they give off an 
odor of decayed organic matter. They are marked by a complete ab- 
sence of crystalline structures, though in some rare cases, as in the 
Bull River phosphate, a distinct concretionary structure is observable. 
The nodules generally contain casts of Eocene shells and, in some 
cases, marine bones and shark teeth. The bones of land animals, 
though mixed with the nodules, are never found embedded in them, 
showing that these bones were probably deposited after the formation 
of the nodules. 
The nodules are found on the bottoms of most of the rivers running 
through the phosphate district, having been washed out of their original 
beds. These river deposits in many cases have proved to be of great 
commercial value. The nodules are, as a rule, of a much darker color 
than those of the land and are often black. They are sometimes very 
siliceous, the separate grains of sand being plainly visible to the naked 
eye. These grains are due to the sand in the marl before it was phos- 
phatized. Such seems to have been the case with much of the Beau- 
fort River phosphate. In some cases, however, the siliceous matter is 
probably due to the replacement of some of the carbonate or phosphate 
of lime in the original nodule by silica, and the result has been to make 
the nodule much harder. Such a silicifying action was probably due 
to the presence of soluble silicates in the river waters. In some 
places, as at the Bolton mine, the land nodules are also very siliceous, 
and possibly became so by having once formed the bottom of a river 
or a bay. 
At least eleven varieties of nodules, differing much in their physical 
character, and often in their chemical composition, may be distin- 
guished among the phosphates taken out of the South Carolina beds. 
These are : 
(1) A jet-black variety with a bright, shining, glossy enamel of the 
same color. It is very rare and generally occurs in small patches. It 
contains numerous fossils and shells. It is found in Parrot Creek 
(see map, PI. I). 
(2) A brown variety with a bright enamel of the same color. It is 
very rich and is found in considerable quantities at the Bradley mine 
and on the land of the Charleston Mining and Manufacturing Company. 
(3) A light-brown variety with little or no enamel. It bleaches white 
when exposed to the sun and is found on the land of the Bradley Com- 
pauy, of the Charleston Mining and Manufacturing Company, and in 
many other localities. 
(4) A light, chalky variety containing many shells and generally 
poorer in quality than the varieties mentioned above. It is very widely 
distributed over the South Carolina phosphate region, and is simply 
marl which has not been so highly phosphatized as the harder and 
darker varieties. 
(636) 
