734 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



"The Hatchetigbee formation, the uppermost formation of the Wilcox group, is composed 

 of beds of brown, purple, and gray laminated sandy clays and cross-bedded sands abounding 

 in characteristic fossils. It is about 175 feet thick in the vicinity of Tombigbee River, but it 

 thins to the east, though otherwise maintaining its distinctive character. These beds have 

 been named Hatchetigbee from a bluff on Tombigbee River." 



The Wilcox group extends eastward into Georgia, where it has not been subdivided into 

 formations and has a small areal distribution. It is best exposed in the bluff of Chattahoochee 

 River at Fort Gaines and probably continues northeastward to Flint River, but it is not easily 

 differentiated from the Midway, except at Fort Gaines. At Fort Gaines the Wilcox and Mid- 

 way are separated by a- distinct erosion unconformity represented by old potholes in the lime- 

 stone of the Midway filled by black sandy clay of the overlying formation. Evidence of this 

 erosion unconformity has not been observed farther east, but this may be due to the imperfec- 

 tion of the natural exposures of the strata. The contact with the overlying Claiborne, where 

 observed, is generally an undulating line of small pebbles or a stratum of coarse sand, and 

 there is no physical evidence of any considerable time interval between the deposition of the 

 two. According to Veatch — 



"Along Chattahoochee River the formation is made up of a sandy glauconitic calcareous 

 shell marl, in places indurated, overlain by dark laminated, often lignitic sandy clays, some 

 beds of which are consolidated into mudstone. To the east, in Randolph County, appears 

 glauconitic clay like fuller's earth, but near Flint River the formation is chiefly sand, in which 

 there are massive beds of white clay. 



"The thickness lying between the Claiborne and Midway at Fort Gaines is about 75 feet. 

 The maximum thickness at any place over the area of outcrop is probably not more than 150 

 feet. This is not in agreement with the thickness on the Chattahoochee, estimated by Lang- 

 don"' at 402 feet, but ia view of the recent determination of strata of Claiborne age * in the upper 

 part of the bluff at Fort Gaines, it is not improbable that a portion of Langdon's 'Lignitic' 

 belongs to the Claiborne formation." 



No outcrops definitely known to represent the Wilcox group occur between Flint River in 

 Georgia and Santee River in South Carolina. In the latter State, on Dr. W. S. Boyd's planta- 

 tion (the old Gourdin plantation), Sloan collected from a silicified rock fossils characteristic of 

 the Nanafalia formation of the Wilcox group. For the formation containing these fossils Sloan 

 has proposed the name Williamsburg. It has probably been identified at Manning. 



West of Alabama, in Mississippi, the Wilcox group has not been subdivided into formations 

 and is known as the Wilcox formation. In this State it is of a more or less sandy character 

 throughout. Crider and Johnson "''^ say : 



"The coarse-grained, unconsolidated sand beds are often interbedded with seams of lignite 

 and white and chocolate-colored clays. The clays of the upper division, as at Grenada, are 

 very dark and may properly be called shale. In the eastern half of the area loosely bedded 

 sands predominate. The western portion, which is a series of irregularly cross-bedded sands 

 and sandy clays, is separated from the eastern by a more or less regular line of white and 

 chocolate-colored clays, which are used for making stoneware. 



"The thickness of the group is estimated from the width of the outcrop to be 750 to 800 feet> 



"The Wilcox covers the largest territory of any formation in northern Mississippi. It occu- 

 pies the entire area lying between the Porters Creek outcrop and the bluffs on the eastern rim of 

 the Yazoo Delta as far south as Grenada. The west edge south of Grenada is a line extending 

 southeast 6 miles east of Winona, west of Philadelphia', and southwest of Meridian." 



In Tennessee, Kentucky, and southern Illinois the deposits of Wflcox age are included in 

 the Lagrange formation of Safford, redescribed by Glenn. Harris *"* has given a r6sum6 of the 

 evidence on which the determinations of the WUcox age of the strata are based. It seems 



o Smith, E. A., Johnson, L. C, and Langdon, D. W., Report on the geology of the Coastal Plain of Alabamai 

 Geol. Survey Alabama, 1894, p. 369. 

 6 Determined by T. W. Vaughan. 



