PENROSE.] 
PHOSPHATES OF SOUTH CAROLINA. 
65 
some places it crops out on the surface and at others is fouud at a much 
greater depth. Under the city of Charleston it is found at a depth of 
over sixty feet. 1 Where the bed does not appear on the surface it 
is covered by alluvial deposits, consisting of clay, sand, or marl, or of 
strata of all three. Occasionally there is a stratum of highly ferrugi- 
nous sand or gravel, sometimes indurated into a regular "hard-pan," 
directly overlying the phosphate bed and from one to ten inches thick 
(Figs. 27, 28, and 29). Sometimes this ferruginous substance has pen- 
etrated the whole bed to a depth of several inches and cemented the 
upper nodules into a solid mass ; while the lower part of the bed is 
much looser and more easily mined. Again the sand overlying and 
intermixed with the nodules has sometimes been cemented together, 
especially in river bottoms, by the action of soluble silicates. Such has 
been the case with the phosphate in parts of the Stono Eiver. Here the 
nodules have in some places been completely permeated by silica and 
form a solid floor on the river bottom. 
Fig. 29. Section 
V.y": : ' ■- t ._ •'•'...'T - ;: " ' a 
; ::'-:M-% ' ■■:' :'•. •V-'-.'H'-'.'-Y '• x^Z 
one of Fishhurne's pits, South Carolina. A, sand ; B. ferruginous sand ; C. phos- 
phate nodules in clay matrix. Scale: 1 inch = 7 feet. 
The following sections by Dr. C. U. Shepard, jr., show the general 
mode of occurrence of the superficial beds of phosphate : 
A. Land deposits : 
I. Soil and subsoil. A few inches to a foot in depth. 
II. A light-colored, siliceous clay, iron stained in places, and containing much fine, 
transparent sand, and minute scales of silvery mica, with little calcareous 
matter, one foot or more in thickness. 
III. (Wanting in the more superficial heds. ) A blue, argillaceous marl, prohahly al- 
tered marsh mud. It does not adhere to the tongue or give an argillaceous 
odor. Fragments of recent shells occur in this deposit. Its depth is ahout 
two feet. 
A thin layer of coarse sand, one to three inches in depth. 
The phosphate nodules in either a loose, siliceous or a tenaceous, bluish or rich huff- 
colored, argillaceous marl, frequently accompanied with abundant fossil bones 
and teeth. The upper nodules are often harder, the lower softer, and at some 
land localities exhibit a gradual transition, by loss of cohesion and decrease, 
of phosphatic contents into 
A marl, highly phosphatic toward the rock-bed, and containing occasionally 
20 to 30 per cent, of phosphates, but at the depth of a few inches containing 
only 10 to 20 per cent, of those constituents. 
1 Dr. C. U. Shepard, jr. : South Carolina Phosphates. 
Bull. 46 5 (539) 
IV. 
V. 
VI. 
