Penrose. J PHOSPHATES OF SOUTH CAROLINA. 61 
central portion of this extensive belt. The Claiborne marls, the Santee 
buhrstones and limestones, and the shell sands of Alabama are the low- 
est beds of this series. Beneath them lie the Pedee marls, which belong 
to the secondary formation and contain fossils resembling those from 
the Chalk of Europe. Immediately over this formation in South Caro- 
lina are the Eocene marls. These beds are very extensively developed 
in that State and are called by Mr. Ruffin "The Great Carolina marl 
bed," which is divided into three divisions, known, in an ascending 
order, as the Santee River, Cooper River, and Ashley River beds. The 
whole formation is about seven hundred feet deep and contains 55 to 95 
per cent, of carbonate of lime. It is one of the most important marl beds 
in the world, on account of both its extent and its agricultural value. The 
upper part of the Ashley marl contains a great number of fossil shark 
teeth and cetacean bones, and has been called by Professor Tuomey 
"the fish bed of the Charleston basin." Overlying' this "fish bed" is 
a deposit of sands and clays of very irregular thickness and containing 
many shells. The bed sometimes runs out altogether and at other 
times is several feet in thickness. 1 It is directly overlaid by a bed con- 
taining many shark teeth and cetacean bones, as well as the remains of 
the mastodon, megatherium, elephant, deer, horse, cow, hog, muskrat, 
and other land animals. Besides these animal remains, the bed con- 
tains very numerous irregularly shaped nodules containing 25 to 70 per 
cent, of phosphate of lime. This is the bed that is worked for phos- 
phates (see Figs. 27, 28, and 29). Sometimes the underlying stratum 
has not existed or has been eroded and the nodule bed rests directly on 
the Eocene marls. It is composed mostly of nodules, associated with a 
much smaller and very variable quantity of bones of land and sea ani- 
mals, buried in a matrix of a variable character. Sometimes they are 
in a bed of highly siliceous sand, containing many flat pebbles of white 
quartz; at other times the matrix consists of ordinary clay or of sand 
and clay mixed. A light blue or green clay is also often seen. 
The nodules are of very irregular shape and vary from the size of 
a pea to that of a mass weighing a ton or more. The larger masses, 
however, are often composed of a number of small nodules cemented 
together. With the nodules and the bones are associated numerous 
phosphatic casts of the interiors of shells, as well as masses, of rare oc- 
currence, which have the appearance of fossil dung (coprolites). The 
nodules, like those of England and of France, are all more or less 
waterworn and rounded and are much bored by marine animals. It 
is generally the harder varieties that are most bored and most irregular 
in shape. This may be due to the fact that, being hard, they preserve 
their original irregular shape and the marks of the boring animals better 
than the softer varieties.- The nodules vary in hardness from 2 to 4 
and have a specific gravity of 2.2 to 2.5. 2 When a fragment is rubbed, 
L -F. S. Holmes: The Phosphate Rocks of South Carolina. 
2 Dr. C. U. Shepard, jr.: South Carolina Phosphates, 
(535) 
