OF SOUTH CAROLINA. 155 
Between these points there are wide gaps that must be filled by future exploration; nor must it 
be supposed that the upper verge of marl and limestone will be confined to the line that I have 
indicated; on the contrary, the true outline will doubtless be more undulating—now extending 
beyond, and again falling short of it. 
This irregular area, occupied by the calcareous strata of the Charleston Basin, is, in length, 
about seventy-five miles, and sixty miles wide. 
Section on the Santee—The lowest point on the river, at which the marl of this section makes 
its appearance, is at Mazyck’s Ferry ; and although it is not seen, at that point, above the surface of 
the water, yet there is every reason to suppose that at no great distance from the bank it occurs 
above the level of the river, covered and hidden, it is true, by superincumbent newer beds. For 
some distance inland from the river the surface is much broken by lime sinks—depressions that are 
due to the solution and washing away of the lime, producing thereby caverns, and finally causing 
the surface to fall in. Now it is obvious that the lime must be elevated above the river, in order to 
allow the springs an outlet, otherwise the lime could not be washed away. 
Marl, mixed with green sand, is found in the bed of Wambaw Creek, but not near the surface. 
‘The next point at which I observed it is Watahaun Creek, at Dr. Tidyman’s, where a white marl 
stone outcrops on the right bank, in large, irregular masses. This little creek is a branch of the 
river that has cut across one of those bends so common in southern rivers. The course of the 
creek is so much shorter (because more direct) than that of the river, that its velocity contrasts curi- 
ously with the sluggish progress of the latter. ; 
Proceeding upwards, the next exposure occurs at McDowell’s, where green sand, mixed with 
soft rich marl is found, forming a thick bed, rising a little above the water level, and extending 
towards the bed of the river. About a mile below the mouth of Echaw Creek, this bed is seen 
again at Moore’s. Near the church, in the bed of the creek, and where the swamp meets the high 
land, white marl stone is found outcropping in thick ledges, of considerable hardness. The surface 
of the country, between Mazyck’s Ferry and Echaw, is far more irregular and broken than one 
would expect, from its position or geological character, and presents a striking contrast to the almost 
unbroken plain on the left bank of the river, which extends to Georgetown. 
The next locality of importance that I examined is at Gourdin’s Ferry: here the green sand, 
which was depressed to the surface of the water, at McDowell’s, is raised above it six feet. The 
height of the section, a short distance below the ferry, is fifteen feet; the upper four feet is a com- 
pact, white marl stone, that is much worn on the surface and exposed edges. The fossils being 
so completely blended in the mass, it is difficult to develope them. 
This passes into a conglomerate of caleareous pebbles and rounded fragments of indurated green 
sand, containing numerous sharks’ teeth, and reminded me of a similar bed, at Wilmington, N. C. 
This dips down stream till it disappears beneath the surface. 
Next below is the bed of green sand, mixed with marl, five feet thick. 'This rests upon a thick 
bed of dark grey, hard marl, altogether different from any seen on the river; and it might have 
been troublesome to determine its true position, had I not found in it casts of that most cosmopolite 
of all Eocene fossils, Cardita planicosta. The length of this section is nearly a mile. The bank 
of the river, at this point, is high and level, and was once the site of a village, built by the early 
