RELATIONS OF LOWER MEMBERS OP COASTAL PLAIN SERIES. 515 



overlain by the Eocene buhrstone to the southward and by the marls of the marine 

 Cretaceous north of the Wateree river. The formation is, however, very irregular 

 in stratigraphy, and clays occur at low horizons at some points, while near Con- 

 garee creek, south of Lexington, I observed the Eocene beds lying on cross-bedded 

 sandstones which merge into a kaolinic arkose on the one hand and into white 

 clays on the other. This kaolinic arkose, as I have termed it, is a remarkable rock. 

 It is pure white in color, and although quite hard it contains a very large propor- 

 tion of true kaolin, intermixed with quartz-sand and much white mica. 



The Potomac outcrops which I visited are at Hamburg, opposite Augusta ; Aiken ; 

 Congaree creek, near Lexington ; Columbia; the region about the junction of the 

 Wateree and Congaree rivers ; Camden, and Cheraw, and I made a boat voyage 

 down the Peedee river from Cheraw to Mars bluff. 



The exposures about Hamburg extend for about a mile along the face of the steep 

 slope which rises from the edge of the flood-plain of the Savannah river to the 

 general plateau level above. To the westward the underlying crystalline rocks may 

 be seen rising gradually above the river, with an irregular shoreline, and the 

 feather edge of the Potomac formation was found near the upper bridge to Augusta. 

 The high plateau has a heavy mantle of typical orange loam of the Lafayette for- 

 mation which extends for some distance west of Hamburg over the crystalline 

 rocks. The Potomac beds consist of a great mass of irregularly cross-bedded, light 

 colored sands containing scattered pebbles of quartz and occasional scattered streaks 

 of sandy pebble beds. To the eastward as the upper beds come in they are seen 

 to be finer grained and to include beds and streaks of light colored clays, sands and 

 sandy clays. Farther down the river there are occasional showings of the forma- 

 tion, notably at Silver blufi" and up Hollow creek, which empties into the river in 

 this vicinity. In these exposures Tuomey has described beds of darker clays, and 

 lignite deposits. 



At Aiken there are excellent exposures of the Potomac beds in the railroad cuts. 

 They extend from the granite in the valley of Horse creek to the heavy mantle of 

 Lafayette formation which caps the high plateau on which the town of Aiken is 

 built. The Potomac materials are similar to those exhibited along the Savannah 

 river, but are all of light color. Some of the lower beds are lithified. At the top 

 there is a bed of white sandy clay, about 30 feet thick, which is locally termed 

 chalk. I was unable to find the western edge of the Eocene buhrstone along the 

 face of the slope at Aiken, as reported by Tuomey, but it is found in wells and 

 depressions a short distance eastward. 



Along Congaree creek, six miles southeast of Lexington station, Potomac clays, 

 sands and sandstones are extensively exhibited, notably at the "Rock house," 

 which is an irregular line of cliffs of sandstone. This sandstone is partly of the 

 kaolinic character described above. Tuomey reported fossite in the upper beds in 

 this vicinity, but stated that they were too fragmentary for identification. I made 

 a long search for organic remains over a considerable area about the " Rock house," 

 but found nothing of molluscan nature. Portions of the soft, kaolinic sandstone 

 show impressions of miqa plates, which are often quite large and so curved as to 

 suggest impressions of fragments of shells, but they are clearly not of organic 

 origin. The edge of the buhrstone was found at a short distance south, lying on 

 white clays and sands of typical Potomac character. 



In the immediate vicinity of Columbia there are several small outcrops of the 

 Potomac beds presenting the usual characteristics. Down the Congaree tliere are 



