3i 



erosion interval, the marine phase of the Potomac being put down 

 at the same time with the true Potomac. To just which one of these 

 two formations the beds at Charleston belong, is a question which is 

 not yet fully determined. Darton seems to consider the greater part 

 of this thickness as belonging to the marine phase of the Potomac ; 

 but the fossils from it have an appearance very similar to that of the 

 fossils of the marine Cretaceous of New Jersey, and the probability 

 is strong that these beds at Charleston, to a considerable depth, are 

 marine Cretaceous resting upon the Potomac. 



South and west of the Santee, the Potomac is overlaid by the 

 Eocene, which also extends northward overlying the marine Cre- 

 taceous and becoming thinner and thinner as it stretches northward 

 until it exists only in widely scattered patches on the irregular sur- 

 face of the Cretaceous marl and gives out altogether before reaching 

 the Waccamaw. At Charleston and thereabout, the Eocene rests 

 upon the marine Cretaceous. In the western part of the Eocene 

 formation in the State, where it outcrops along the line from Aiken 

 to within a few miles of Columbia, the lowest beds are composed of 

 buhrstone and argillaceous beds. This Buhrstone formation, accord- 

 ing to Darton, 1 appears to lose its characteristics in the extreme 

 eastern part of the State and becomes a marl. According to the 

 same writer, the thickness of the Eocene members at Charleston is 

 about 370 feet, and are supposed to extend upward to about 60 feet 

 from the surface. Now, elsewhere in this chapter, it is pointed out 

 that the Pliocene has been reported from a depth of 65 feet at 

 Charleston. If this latter statement be true, then the Eocene must 

 be somewhat farther down still — maybe very little farther. Besides 

 the Buhrstone the Eocene beds consist of marls of various kinds, 

 which have been put into two classes by Toumey and others — viz., the 

 Santee beds, which are light colored, and the Ashley and Cooper 

 beds, which are darker in color. 



What small, thin patches of Miocene have been left after erosion 

 are in the northeastern part of the State, in Florence, Sumter, Dar- 

 lington and Marion counties. It occupies depressions in either the 

 Eocene or the marine Cretaceous. The beds are rarely more than 

 thirty feet in thickness, and are generally much thinner. They con- 

 sist of sands and marls and contain many species of molluscan fos- 

 sils. Other small areas of it have been found in the southern part 



1 "Notes on the Relations of Lower Members of the Coastal Plain Series in 

 South Carolina" (Geol. Soc. Amer., Bull., Vol. VII, pp. 512-18, 1896). 



