RELATIONS OF LOWER MEMBERS OF COASTAL PLAIN SERIES. 513 



determined, several very important features were not ascertained. These relate 

 mainly to the lower members which lie on the east-dipping floor of crystalline rocks. 



Statement op former and present Views 



During the past two years I have given considerable attention to the question of 

 artesian water supply on the Atlantic slope, and last winter found it necessary to 

 visit eastern South Carolina for a brief study of the conditions in that region. As 

 the lower formations of the Coastal Plain series promised to be important water- 

 bearers I paid special attention to their characteristics and relations. From the 

 descriptions by Tuomey it would appear that the Eocene formation includes in its 

 lower portion a series of clays and sands which lie directly on the granite in the 

 southern portion of the state, while to the northward the Cretaceous marls emerge 

 from beneath the edge of medial Eocene beds. The formations underlying the 

 Cretaceous marls were not fully described, and apparently they were also supposed 

 to pass under the overlapping series of sands and clays of the lower Eocene, which 

 is stated to lie directly on the granite in all the region south of the Wateree river. 



From a study of this problem in the field I find that the so-called basal members 

 of the Eocene are not Eocene at all, but are representatives of the Potomac forma- 

 tion, and this formation extends northward beneath the marine Cretaceous marls, 

 of which the edge emerges from under the Eocene north of the Wateree river. 

 Thus it was found, as suggested several years ago by McGee, that there is a con- 

 tinuous sheet of Potomac formation lying on the crystalline rocks throughout South 

 Carolina. To the southward it is overlain by the Eocene formation and to the 

 northward by a gradually increasing thickness of the marine Cretaceous marls, 

 which also thicken to the southeastward out under the Coastal Plain, as shown by 

 their great mass in the wells at Charleston. 



Coastal Plain Sections in South Carolina 



In the three sections comprised in figure 2 (page 514), I have attempted to present 

 the matter as clearly as possible and to bring together all available data on the 

 structure of the Coastal Plain portion of South Carolina. 



The new information in these sections is derived from a study of the outcrop belt 

 of the Potomac formation and from records and samples of artesian well borings. 

 As there is now considerable prospect that wells will soon be bored in many places 

 in eastern South Carolina, it is probable that at no distant time data will be ob- 

 tained which will fully illustrate the underground structure of the region. 



The Formations and their Characteristics 



The principal formations of the Coastal Plain series in South Carolina are as fol- 

 lows : 



Formations. Characteristics. 



Columbia. Gray sands, etcetera. 



Lafayette. Orange loams. 



Miocene. Sands and marls. 



Eocene. ^ Buhrstone below, marls above. 



Marine Cretaceous. Marls, sands and clays. 



Potomac. Sands, sandstones and clays. 



