Penrose.) PHOSPHATES OF SOUTH CAROLINA. 63 
(5) A dark grayish- black variety with little or no enamel. It is very 
siliceous and contains many shells. It is generally found in rivers, and 
is especially characteristic of the Stono Elver district. 
(0) A gray variety composed of a mass of shells and transparent sili- 
ceous sand, cemented together by a phosphatic cement. Sometimes 
shark teeth are included in the mass. At times it is hard and compact, 
and at others it is loose, soft, and porous. Such varieties are found in 
large quantities in the Beaufort River. They are often mixed with a 
much better quality of nodule which raises the average phosphatic con- 
tents. 
(7) A dark-gray, phosphatic conglomerate, in which the pebbles arc 
quartz and feldspar, varying from the size of a mustard seed to that of 
a buckshot. The matrix is a dark- gray, phosphatic marl. This variety 
is very rare in South arolina, but is found in small quantities in the 
Bull River district. 
(8) Nodules having a black enamel and alight or dark gray interior. 
They contain many .shell casts and are found in the Coosa w Kiver and 
on the Edisto River at Fishburne's mine. 
(9) A variety consisting of a mass of concentrically laminated nodules 
cemented together with a matrix of marl containing many shells. This 
variety is rare and was found only in the Bull River. It is generally 
rich in phosphatic matter. 
(10) A ferruginous, rusty-brown variety, very siliceous and of poor 
quality. 
(11) Brown or black masses having the general appearance of fossil 
dung (coprolites) and probably of that nature. They are hard and very 
rich in phosphate of lime. Real coprolites are of rare occurrence. 
Occasionally large, flat, non-concretionary masses are found, which 
are highly phosphatized on the upper side, while toward the lower side 
the mass grows poorer and poorer in phosphates, until it differs but 
little in composition from the underlying mark In such cases the phos- 
phatized part of the rock is of a darker color than the other part. 
The upper side is also much smoother and harder than the lower side, 
which is often very jagged and is sometimes almost as soft as the under- 
lying marl. This formation shows that in some cases at least the piios- 
phatization has gone from above downward. Such a process is also 
proved by the fact that the marl immediately underlying the phosphate 
bed contains sometimes 20 to 30 per cent, of phosphate of lime, 1 while 
this quantity decreases with the depth until, at a few inches below the 
nodule bed, it contains only 10 to 20 per cent. According to Professor 
Holmes, the marl is much richer in phosphate of lime in those places 
where it is overlaid by nodules than where no nodules are found. 
Some of the varieties of nodules have been found to grow poorer in 
phosphoric acid as the center of the mass is approached. This is espe- 
l Dr. C. U. Shepard, jr. : South Carolina Phosphates. 
' (oil) 
