736 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



The Gosport sand, according to Smith/*'" "so far as yet known, does not appear in any other 

 of the Gulf States but embraces the strata of the Claiborne group lying between the top of the 

 Lisbon and the base of the St. Stephens. The beds are in general highly glauconitic sands about 

 30 feet in thickness at the Claiborne and Gosport bluflfs and include the fossUiferous greensands 

 which have made the name Claiborne famous and which have furnished the greater part of the 

 Claiborne fossils described and figured by Conrad and Lea. While this division, as above men- 

 tioned, is not known in Mississippi, Louisiana, or Texas, yet its importance in Alabama, from 

 the historical point of view and because of the great number and variety and beautiful state of 

 preservation of its fossils, is such as to compel mention and a distinct name. This member of 

 the Claiborne group has been observed at a number of localities in Monroe, Clarke, Choctaw, 

 and Washington counties. The name is from Gosport, a landing on the Alabama River a few 

 miles below the Claiborne Bluff." 



In Georgia,*" although in a general way the correlatives of the formations of the Claiborne 

 group in Alabama may be recognized, the extension of the formational nomenclature used in 

 that State is inappropriate, for the group is not naturally divisible into the same units. The 

 divisions recognized are the Barnwell sand and the McBean formation, with the Congaree clay 

 member at its base. 



The McBean formation rests unconformably upon strata of Lower Cretaceous age east of 

 Ocmulgee River, and tongues of the formation extend to the crystalline rocks of the Piedmont 

 area. Between Flint and Chattahoochee rivers the McBean rests upon the Wilcox formation, 

 with evidence of an erosion unconformity along Chattahoochee River in the vicinity of Fort 

 Gaines. In eastern Georgia the formation is overlain by the Barnwell sand, the relations 

 between the two formations being somewhat obscure. Along the northern margin of the areal 

 occurrence of the Barnwell sand there is evidence of an unconformity of slight time importance, 

 but farther south the sand seems to rest upon the McBean formation with conformable relations. 

 It seems probable that near the close of McBean time there was an uplift which brought the 

 northern margin of the area of Claiborne deposition above sea level, permitting erosion to take 

 place along the margin of the emerged area, while deposition continued in the area which 

 remained under water. The formation consists mainly of clays, in places having the character 

 of fuller's earth, shell marls, sandy limestones, or calcareous glauconitic sands. The maximum 

 exposed thickness of the formation occurs at Shell Bluff, on Savannah River, where 115 feet of 

 strata were measured. Outcrops of the formation occur in an extremely irregular belt that 

 extends entirely across the State and ranges from a few miles to 25 mUes or more in width. 

 East of Flint River exposures are known in Columbia, Richmond, Burke, McDuffie, Jefferson, 

 Glascock, Washington, Baldwin, Wilkinson, Jones, Twiggs, Bibb, and Houston counties. 

 There are also exposures on Flint River in eastern Sumter county and along Chattahoochee 

 River from Fort Gaines southward. 



The Congaree clay member in eastern Georgia rests directly upon the Lower Cretaceous, 

 the contact being marked by conspicuous erosion unconformities. It is conformably overlain 

 by the claj^s and marls of the McBean formation or by the Barnwell sand, either passing into 

 the latter hy gradation or in some exposures being separated from the former by unconformities. 

 Lithologically the Congaree clay member consists of fuller's earth in which are small lenses and 

 pockets of sand; in some places it contains large amounts of disseminated lignitic matter and 

 thin beds of lignite. Tlie thickness of tliis member is at least 100 feet. There are numerous 

 outcrops of the Congaree clay member from Grovetown soutbwestward along the "fall line" 

 to Bibb and Twiggs counties. It is confined to the northern part of the area of the outcrop of 

 the McBean formation, but no sharp lines separating the member either from the marls of the 

 McBean formation or from the overlying Barnwell sand can be drawn. Clays and fuller's 

 earth of the same general character as the Congaree clay member also occur in the vicinity of 

 Chattahoochee River near the northern margin of the area of outcrop of the McBean formation. 



The Barnwell sand directly overlies the McBean formation and is in contact with both the 

 marls and the Congaree clay member. Along the northern margin of the Barnwell sand area 



