188 GEOLOGICAL SURVEY 
perpendicular bluff, thirty feet in height, composed principally of yellow sand. At the base, a bed 
about eight feet thick is exposed, which is made up of sand and broken shells. At first sight it 
had the appearance of being thrown up by the waves into its present elevation; but a bed of blue 
mud, which I found overlying the shells, convinced me that its surface was once at the level of 
tide, and that its present position, eight feet above it, is the result of a regular uplift, and not the 
effects of waves. This is the highest elevation at which I have seen the fossilliferous bed of the 
P. Pliocene of the State. 
The fossils that I found here are Arca ponderosa, A. pexata, Mactra lateralis, M. similis, Oliva 
litterata, Donax variabilis, and Gnathodon cuneatum. 
There are other localities around Georgetown, and fossil shells of the formation have been met 
with, during the excavation of the Winyaw Canal, showing that this region is underlaid by it. It is 
exposed on the Santee, below Mazyck’s Ferry, at Fairfield. The bed at this place must correspond 
with the stiff, blue clay that is penetrated in the wells in Charleston. It is a tenacious and com- 
pact clay, containing but few fossils, and those always with the valves united: Mactra lateralis 
and Pinna seminuda were among the most conspicuous. 
In Christ Church Parish, Charleston District, there are several exposures where this bed comes 
so near the surface as to be within the reach of the plough. The mazrl is sufficiently calcareous to 
be of great economic value. In one instance I found a bed of white calcareous mud, such as is 
formed by the disintegration of corals. 
The next locality to be noticed is one which is found about a quarter of a mile from the river, at 
Bee’s Ferry, on the Ashley. A bed of blue clay, containing Mactra lateralis, is exposed in an 
excavation for a well. This bed, by actual measurement, is elevated above high-water level about 
five feet, and is one of the few instances presented for ascertaining the amount of elevation of the 
P. Pliocene. It is true that we do not know the actual depth below high-water at which these beds 
were deposited, but as they contain generally such shells as Lutraria, Pholas, Mactra, Arca, and 
Cardium, that bury themselves in the sand and mud between high and low water line, on the 
shores of Charleston Harbor, at the present time—it is safe to conclude that the elevation of 
the P. Pliocene does not exceed, along the whole line of the coast, eight feet. There is no sudden 
break any where separating it from the beds now in progress of deposition, for it dips gently 
under the waves of the ocean, and the fossils are often found mingled with living species. 
Prof. L. R. Gibbes pointed out to me another locality, lower on the river. The top of the stratum 
is at high-water mark, and is about three feet in thickness, composed of sand and shells well pre- 
served, although the valves are generally disconnected. 'The proportion of those in juxtaposition 
is about equal to what one might find among the shells thrown up on the beach. This rests on a 
band of fine laminated clay, six inches thick, which is underlaid by blue, stiff mud, with layers of 
sand between the lamine, in which are embedded numerous small shells of the genus Mactra. 
The superincumbent stratum is fifteen to twenty feet thick, composed of fine sand, without any 
marks of diagonal bedding. The interesting section presented here is about 200 yards in length. 
I collected about twenty-six species of fossils common to other beds of the formation, and among 
them I saw, for the first time, Zucina Burnetti, Brod. which is now found, living, on the coast of 
California. 
This fossilliferous bed underlies the whole coast, and is seen wherever the streams remove the 
