daeton.] SOUTH CAROLINA. 209 
MARINE CRETACEOUS. 
This is mainly a shell marl, which is at or near the surface in Horry, 
Marion, Florence, Williamsburg, and Georgetown counties, but sinks 
beneath later formations to the southward. With the marl there are 
associated marlstone, soft gray shales, and sands, which are all fre- 
quently exposed along the Pedee and Waccamaw rivers. In its ex- 
tension to the south under the Eocene and other formations this series 
increases greatly in thickness and probably comprises the beds from 
about 450 to at least 1,950 feet in the Charleston wells. As suggested 
above, it is possible, however, that these lower beds in this well include 
some marine representatives of the Potomac formation. 
These formations include the buhrstone and a series of overlying 
marls, which cover a wide area in the southern section of the State. 
To the northward, in Williamsburg and Marion counties, they thin out 
and are represented by only thin, scattered outliers. The western edge 
of the buhrstone, which is usually the basal member of the formation 
westward, passes from Aiken to within 10 miles of Columbia, and thence 
to the eastward to below the junction of the Congaree and Wateree 
rivers. In the well at Charleston the Eocene members have a thick- 
ness of about 400 feet, and are supposed to lie about 60 feet below the 
surface. They there consist of marls of various kinds, which are 
mainly argillaceous above and calcareous below. The buhrstone is a 
hard, siliceous rock, often tilled with shells, which constitutes the basal 
Eocene member in the outcrops along the western margin of the forma- 
tion as above outlined. The overlying marls and marlstones are known 
as the Santee beds and the Ashley and Cooper beds. Their western 
margins lie in succession to the east of the buhrstone outcrop, and they 
thicken gradually to the eastward, as seen in the Charleston well (see 
PI. XVIII). The Santee beds are mainly light-colored marls, with some 
beds of marlstone of considerable extent, and the Ashley and Cooper 
marls, which outcrop quite widely in the basin of the Ashley and 
Cooper rivers, are of darker color. 
MIOCENE. 
These deposits consist of sands and marls, which occur in scattered 
areas, mainly in the northeastern and eastern counties. Their thick- 
ness is usually not over 30 feet, and they lie on an irregular surface of 
the Eocene, or marine Cretaceous formations. 
LAFAYETTE FORMATION. 
This is a superficial mantle of orange loams and sands which covers 
the higher plateau regions at elevations of about 050 feet along the 
western border of the Coastal Plain province. There it has a thick- 
Bull. 138 14 
