144 GEOLOGICAL SURVEY 
shallow, at first sight reminding one of a circular race-course. They are numerous in Barnwell 
District, and may be seen between the Court House and Aiken; some filled with water and others 
dry. Between Orangeburg and Rocky Swamp, on the Edisto, there are several—some of them 
many acres in extent, quite level, and having the edges somewhat raised above the ordinary sur- 
face. They have quite an artificial appearance, and it was not before I had examined the ponds, 
above Vaucluse, on Horse Creek, that I was enabled to make them out. 
At the latter place the ponds are situated at a considerable elevation above the valley of the 
creek, having under-ground vents opening on the sides of the hills, in the form of what are called 
“boiling springs,” that is, springs that bubble up with some force. No inconsiderable amount of 
fine sand is thrown out by these springs, and conveyed downwards by the streams. 
Now it is obvious that so long asa pond supplies more water, derived either from rains or springs, 
than these vents can carry off, it will remain permanent; and, on the other hand, when the 
vents, from any cause, become too great, or will discharge more than the supply, that the ponds 
must be drained. Should these under-ground drains afterwards become choked, or by any means 
stopped, the ponds would again be filled; and such alternations as this I have seen in Barawell— 
where roads once passed through dry hollows, that are now permanent ponds; and the stumps of 
pine trees, standing in the water, show that they had long been dry, 
Other examples were pointed out to me of ponds of considerable extent that were known for 
years with water, but becoming dry, now present the depressions of which I have spoken. ‘The 
circular form of these depressions is easily accounted for. Any sheet of water, in so incoherent a 
soil as that covering the surface of this region, however irregular its outline, would soon become 
circular, because the projecting irregularities would be washed away. Neither is it difficult to un- 
derstand why the depth should be so slight, and the form not conical, like lime-sinks. The sandy 
surface, when completely saturated with water, becomes almost semi-fluid, and as sand is removed 
by the drain, of course this semi-fluid mass flows in towards the centre, and, by extending the cir- 
cumference, prevents any material change in depth. And after the pond has become dry, this ten- 
dency towards the lower points still continues until the surface becomes nearly level. Of course the 
clearing and cultivation of the land are constantly affecting these accumulations of water. 
It will be seen that Aiken, including a few miles around the village, presents peculiar facilities 
for the study of the Buhr-stone formation of the State. From the summit to Horse Creek, the 
perpendicular height is 200 feet, and in this thickness we have all the members of the Buhr-stone 
formation. 
The granite ridge that extends across to Columbia is covered by beds of white sand. Where 
these are removed, on the hill-sides, the underlying red loam is exposed, which forms a better soil. 
On the ridge, above the head waters of Edisto, the surface is level, as far as Lexington, and in 
summer the deep sands make travelling exceedingly laborious. 
From Aiken to South Edisto the country sinks gently, but the ridge between the two rivers is 
elevated, and is an uninterrupted pine barren; the beds of sand, however, are not so deep, and the 
red loam and mottled clays come more frequently to the surface. 'Towards the head springs of 
Lightwood Creek the white Eocene grit and sandstone are left upon the tops of the ridges, in thick 
ledges, interstratified with beds of sand and porcelain clay. These ledges are ten or twelve feet in 
thickness, and, from the unequal resistance they present to destructive atmospheric agencies, they 
