136 GEOLOGICAL. SURVEY 
Fig. 26. D 
Section from Britton’s Ferry to Mar’s Bluff. 
A.—Britton’s Ferry. B.—Giles’s Bluff. C.—Birch’s Ferry. D.—Mar’s Bluff. 1—Tertiary Beds. 2—Marl, over- 
lying marl stone. 3.—Marl stone. 4.—Beds underlying the marl stone. 5.—Shale. 6.—Sand. 
The next exposure, on the banks of the river, is at Birch’s Ferry, where a fine section, 200 yards 
in length, and 15 to 20 feet in height, is laid bare. The fossilliferous bed of marl stone, (3, Fig. 26) 
has disappeared. The stratum immediately below it forms the greater part of the bluff, and the 
black shale makes its appearance, for the first time, as a distinct and well characterised stratum. 
It is seen, at the southern extremity of the section, emerging with a gentle dip from the water. I 
found here Ostrea cretacea pretty common, and Belemnites Americanus, in most astonishing abun- 
dance. 'The lower part of the perpendicular bluff is only accessible by means of a boat; but when 
the ledge of shale is reached one can then examine that part of the section with ease. The bed 
overlying the shale, which I have already said constitutes the greater part of the bluff, is a soft, 
dark gray marl, and, for the first ten feet, is filled with Belemnites, which project from it in every 
direction. It looks as if some persons had amused themselves by driving as many as possible into 
the face of the bluff. Hundreds have fallen down and are strewed along the edge of the water. 
This is certainly the most extraordinary locality of this fossil in the United States, or perhaps in 
any country. I looked in vain for any other remains of the Cephalopod, that must have existed 
on this spot in such vast numbers. 
The substance that I have denominated shale is a black, laminated clay, quite smooth and unc- 
tious to the touch, but is seldom so hard as not to yield to the knife. There is a black mud, which 
is found in the marshes and other places in Charleston harbor. It is called “pluff mud,” and when 
dry it resembles this shale more nearly than any substance that I have seen. 
A half mile west of the river the marl stone stratum outcrops, on the road side, near Leggett’s 
mill-branch. It contains but few fossils, and among them I found Anomia argentaria and Belem- 
nites ; and this is the only place, besides Birch’s Ferry, that I have found this fossil. 
At Gordon’s old mill the shale occurs, and is overlaid hy masses of silicified shells. I identified, 
among these, Cardita planicosta and Turretilla Mortoni, two characteristic Eocene fossils—show- 
ing the existence of this formation on the Peedee. 
The calcareous beds of the Cretaceous formation extend a short distance above the mouth of 
Jeffrey’s Creek, and after that the shale alone is found in the river bluffs. It continues to rise, and 
the underlying sandy beds make their appearance. 
The noted locality, Mar’s Bluff, is made up of these beds, in the following order, beginning at the 
base: Blackish clay and sand, five feet, overlaid by beds of sand, showing oblique lamination ; 
these are succeeded by heavy beds of shale, almost unmixed, which are capped by alternating 
bands of shale and sand. 
