134 GEOLOGICAL SURVEY 
most eastern locality of the cretaceous rocks in the State. From this it rises gradually towards the 
’ North-west, till it attains its greatest elevation, at Mar’s Bluff, on the Peedee, which is about 150 
feet above tide. Right and left of the river it is covered by the Tertiary formation, yet it seems to 
be at no great depth below the surface, for it is exposed near Darlington Court House and on Black 
Creek. A line drawn from the Court House, south, to the mouth of Sparrow Swamp, on -Lynch’s 
Creek, and thence to Black River, below King’s 'Tree, will mark the western boundary of this for- 
mation, in South Carolina. It now sinks beneath the Tertiary of the Santee and is not seen again. 
At Buck’s Saw-mills, on the Waccamaw River, nine miles below Conwayboro, is the lowest 
point, in Horry, where it is seen. Here some bands of silicious, slaty rocks are found, at low water, 
that must be referred to this formation, although I found no fossils in them. On the banks of the 
lake, at Conwayboro, beds of indurated calcareous clay occur; and on the opposite bank of the 
river, on Mr. Wilson’s land, similar beds are found, which correspond in position and mineral char- 
acter with certain cretaceous beds. 
At Harper’s Landing, a few miles higher, on the river, they rise above the surface of the ordi- 
nary state of the river, eight or ten feet; they are composed of a grayish, sandy clay, but slightly 
calcareous, containing Hrogyra costata. These beds are overlaid by a stratum of upper Tertiary 
marl, abounding in fossils. The fine section at this place is one mile and a half in length. 
At Waller’s it is seen again, but rising above the river only two or three feet, showing a con- 
siderable amount of undulation in the surface. On Tilley’s lake, at Nixon’s, it occupies the same 
position, and is elevated about the same height above the river. At both of these places Hxrogyra 
costata is the only fossil present. 
Other localities occur as high up the river as Royal’s Landing, but they present nothing to dis- 
tinguish them from these. They are every where overlaid by Pliocene beds. 
The lowest point on the Peedee where the Cretaceous rocks are exposed, is at Yahany Ferry. 
At low water beds similar to those on the Waccamaw are seen here. About ten miles higher 
up the river, at Petersfield, a bluff four or five feet in height is composed of dark gray beds of sand 
and clay, with white, irregular fragments of marl; the mass, however, is but slightly calcareous. 
Britton’s Ferry, still higher, exhibits a fine section, ten feet in height. About seven feet of the 
upper portion of it is composed of a mixture of sand and clay, approaching loam, with very finely 
comminuted shells interspersed throughout the mass. These beds, although quite dark when wet, 
become light gray or ash color, when dry. Underlying this, and immediately on the brink of the 
river, is an indurated bed, which Mr. Ruffin has called marl stone. It is about three feet thick, 
and much more calcareous than the superincumbent bed, which is washed away three or four 
feet, leaving this standing out, and forming a convenient terrace from which the section may be 
examined. I found here Exogyra costata, Gryphea mutabilis, Anomia argentea, and Cucullea 
vulgaris. 
ComMposITION OF THE BeEps. 
Upper Stratum. Marl Stone. 
Carbonate of Lime. ..... POON. eae 55.00 
Silica Se ee ae A000) Ah a eee 30.25 
Alumima and (Ox. Irons. 30:50) 2 ee eeaenenel 13.60 
