10 CRETACEOUS DEPOSITS OP THE EASTERN GULF P.EGION. 



lapping Eocene beds and do not reappear at the surface until they reach the valley of Peedee 

 River in eastern South Carolina, in which region, and also to the northeastward in North 

 Carolina, exposures are common along the streams. 



PAST AND PRESENT INTERPRETATIONS. 



LOWER CRETACEOUS. 



The basal portion of the rocks of the Coastal Plain in the region included between the Alabama 

 Valley in Alabama and the Roanoke Valley in North Carolina is composed of highly cross- 

 bedded arkosic sands, in general of coarse texture, with subordinate interbedded laj T ers and 

 lenses of light-colored clays of greater or lesser purity, reaching an estimated maximum thickness 

 of 500 to 600 feet. These have been regarded as the eastward continuation of the Tuscaloosa 

 formation by the Alabama and Georgia geologists. 1 They have been designated the "Ham- 

 burg beds" by Sloan 2 in South Carolina and the "Cape Fear" formation by the writer 3 in 

 North Carolina. These beds are separated by unconformities from the overlying Black Creek 

 formation in the Carolinas and from the overlying Eutaw formation in the Chattahoochee and 

 Alabama river regions in Georgia and Alabama. (See PI. I, B.) 



In 1906 the exposures of these beds on Chattahoochee River below Columbus, Ga., were 

 examined by the writer, and during subsequent years numerous localities in Alabama and 

 Georgia were visited by him. Various considerations, based on physical evidence, led him to 

 conclude that the terrane is older than the Tuscaloosa formation, that it probably corresponds 

 to the "Hamburg beds" of South Carolina and to the "Cape Fear" formation of North Caro- 

 lina, and that it is probably of Lower Cretaceous age. E. W. Berry, who later visited a num- 

 ber of the localities in company with the writer, concurred in these views. 



The first and strongest argument in favor of this interpretation was the existence of a 

 distinct unconformity separating these beds from the overlying Eutaw formation. This was 

 noted unmistakably at McBride Ford on Upatoi Creek, Chattahoochee County, Ga. ; at the 

 Lumpkin road bridge over Upatoi Creek a few miles above its mouth; on Chattahoochee River 

 just below the mouth of LTpatoi Creek and at Broken Arrow Bend, 9 miles below Columbus, Ga. ; 

 on the Seale road 4 miles southwest of Columbus in Russell County, Ala. (PI. I, B); and on Ala- 

 bama River 5 miles above Montgomery, Ala. The unconformity was also questionably noted 

 at several places intermediate between those named. No such unconformity is known to exist 

 between the true Tuscaloosa formation and the overlying Eutaw formation in central or western 

 Alabama or in Mississippi. 



The beds differ from the true Tuscaloosa deposits in the following respects: The sands 

 contain a large percentage of white kaolin grains, which render them arkosic; the layers and 

 lenses of clay are massive, being thus in contrast with the laminated beds so common in the 

 Tuscaloosa (PI. I, ^4); and the beds lack identifiable fossil plant remains except at one locality. 

 On the other hand, in all these characters they strongly resemble the "Hamburg beds" of South 

 Carolina and the "Cape Fear beds" of North Carolina, and it was this fact, together with their 

 apparent continuity with the deposits of the Carolinas, that led to the belief that they are 

 synchronous with those deposits. 



The "Cape Fear" formation is separated geographically from the Cretaceous deposits to 

 the north in Virginia by an overlap of Miocene beds. However, in all their physical characters 

 the "Cape Fear" materials bear a close resemblance to the Patuxent formation, which forms 

 the basal division of the Potomac group in Virginia and Maryland. On account of this physical 

 similarity and because of their supposed buried connection with the Virginia Patuxent, the 

 application of the name Patuxent has been extended to include these arkosic beds* in North 



1 Langdon, D. W.. Variations in Cretaceous and Tertiary strata of Alabama: Bull. Geol. Soc. America, vol. 2, 1890, pp. 587-606. Vcatch, Otto, 

 Second report on the clays of Georgia: Bull. Georgia Geol. Survey No. IS, 1909, pp. 82-106. 



' Sloan, Earle, Clays of South Carolina: Bull. South Carolina Geol. Survey, 4th ser., No. 1, 1904, pp. 72-75; Handbook of South Carolina, State 

 Dept. Agr., Com., and 1mm., 1907, pp. 85- 58. 



3 Stephenson, I.. W., Some facts relating to the Mesozoic deposits of the Coastal Plain of North Carolina: Johns Hopkins Univ. Cire., now ser., 

 No. 7, July, 1907, pp. 93-99. 



' Stephenson, I.. \Y., The Cretaceous formations [North Carolina): North Carolina Geol. and Econ. Survey, vol. 3, 1912, pp. 83-111. 



