RELATIONS OF LOWER MEMBERS OF COASTAL PLAIN SERIES. 517 



of the Newark formation. The Potomac beds begin at a depth of about 110 feet, 

 as nearly as I can fecoi^nize them, and consequently have a thickness of about 500 

 feet. They consist of gray sands in greater parts, presenting considerable variety 

 in coarseness. Considerable lignite was reported, but no clay appeared in the few 

 samples of borings which were saved. For the well at Marion I was unable to 

 obtain many definite data, but learned that the lower members of the Coastal Plain 

 series were alternating beds of sand and tough clay, and that their floor of crystal- 

 line rock was found at a depth of 700 feet. At Darlington the Potomac sands were 

 found underlying the Cretaceous marls, but the depth of the contact was not ascer- 

 tained. At Orangeburg the Potomac sands were entered for some distance in a 

 well which has a depth of 1,160 feet. I was only able to obtain meager informa- 

 tion for this well, and could not determine the nature or age of the beds which lie 

 next above the Potomac sands, but I should expect them to include a considerable 

 portion of the marine Cretaceous marls which extend from 430 to over 1,800 feet 

 in the Charleston well. I might here add that I am strongly inclined to believe 

 that at least a portion of the lower beds in the Charleston wells may represent an 

 offshore phase of the Potomac formation. However, as higher Cretaceous niol- 

 luscan remains were reported from a depth of 1,955 feet in the first well, tlie 

 water-bearing sands and sandstones from 1,960 to 1,980 feet may be the top of the 

 Potomac formation. 



Although I observed plant remains in the Potomac beds at many points * which 

 would no doubt settle any question as to the age of the beds, I have depended en- 

 tirely on the structural relations and physical characteristics for my correlation of 

 the formation. There could not be any doubt as to the continuity of the great 

 series of sands, clays and sandstones which underlie both the Eocene buhrstone 

 and the Cretaceous marls and lie on the surface of the crystalline rocks. As this 

 series lies below quite old marine Cretaceous and above the Newark formation, 

 the most obvious correlation would be with the Potomac formation, which occupies 

 this position for hundreds of miles along the Atlantic slope, and moreover their 

 physical characteristics fully bear out the correlation. Of course in speaking of the 

 Potomac formation I refer to that formation as a whole, comprising the Tuscaloosa 

 beds, which I believe are eventually to be separated as an independent formation. 



Marine Cretaceous Formation 



I have nothing of general interest to add to the statements of Tuomey regarding 

 the Cretaceous marls and clays, for I did not extend my observations very far into 

 their area. The formation appears to thin out before reaching the Wateree river, 

 and on Black river it appears to be buried under the Tertiary, excepting possibly 

 for a short distance near Kingstree, where it is indi(!ated on the geologic map issued 

 in 1883. The enormous expansion of the formation in the well at Charleston is a 

 rather surprising feature, but, as above suggested, it is possible or even probable 

 that the lower beds in this well are offshore deposits of Potomac age. 



Eocene Formations 



The lowest Eocene beds westward are the buhrstone and some argillaceous marls 

 which underlie the buhrstone at certain localities. To the eastward there are sev- 



* I have been informed by Professor Lester P. Ward that he has discovered plant remains of 

 Potomac age in the extension of these beds in North Carolina oh the Cape Fear river and also at 

 various points in eastern Alabama. 



LXII— Bull. Geol. Soc. Am., Vol. 7, 1895. 



