PAST AND PRESENT INTERPRETATIONS. 13 



position to the lower two-thirds or three-fourths of the Tombigbee as mapped south of the line; 

 indeed the sections given as typical of the Eutaw He within these northward Tombigbee 

 representatives. 



Western Alabama. — The Eutaw group of Hilgard in Mississippi represents all of the 

 Tuscaloosa formation and a part of the Eutaw formation as subsequently defined by Smith 

 and Johnson in Alabama. They described the Tuscaloosa formation as consisting of at least 

 1,000 feet of "purple and mottled clays interstratified with white, yellowish- white, pink, and 

 fight purple micaceous sands, and near the base of the formation dark-gray, nearly black, 

 thinly laminated clays with sand partings." 



The Eutaw formation is described as "a series of laminated sands and sandy clays at 

 least 300 feet in thickness." 



If only those parts of the area in Mississippi immediately west of the Alabama line, mapped 

 by Hilgard respectively as Eutaw and Tombigbee, are considered, his Eutaw corresponds 

 almost exactly to the Tuscaloosa formation of Smith and Johnson, and the Eutaw of those 

 authors corresponds to the Tombigbee sand of Hilgard. However, the sections of the Eutaw 

 described by Hilgard, all of which are north of Columbus in Mississippi, do not correspond to 

 the Tuscaloosa formation, but, as previously stated, represent a part of the northward exten- 

 sion of the Tombigbee as mapped, and hence actually correspond in sttatigraphic position to 

 a part of the Eutaw of Smith and Johnson. 



The essential differences between the Tuscaloosa and Eutaw of Smith and Johnson may 

 perhaps best be stated as follows: The Tuscaloosa consists of a succession of sands, clays, and 

 gravels of probable estuarine and shallow-water origin, characterized by irregularity of bedding, 

 and, where the conditions for their preservation were favorable, by the presence of fossil leaves 

 (PI. II, A); the Eutaw consists predominantly of glauconitic sands of marine origin, which in 

 approximately the lower two-thirds or three-fourths of their thickness contain subordinate 

 lenses of dark clay and exhibit lamination and fine cross-bedding (PI. II, B), and in the upper 

 one-third or one-fourth are made up of massive beds of glauconitic sand, with calcareous sand 

 beds in the extreme upper part (PL III, A). So far as known no structural break exists between 

 the Tuscaloosa and Eutaw formations, sedimentation apparently having been continuous from 

 the one to the other. Nor has it been possible to recognize any sharp lithologic line of separation 

 between them, the change from the one kind of sedimentation to the other having been 

 transitional. 



The Mississippi representatives of the Eutaw formation of Smith and Johnson include, as 

 previously stated, all of the Tombigbee sand and a part of the Eutaw group of Hilgard. Although 

 the width of the Tombigbee belt as mapped by Hilgard immediately west of the Alabama line is 

 15 to 18 miles, corresponding to a thickness of 400 or 500 feet, the actual sections given by him 

 in this part of the area are all near the western border of the belt and probably include only 

 about the upper 150 or 200 feet of the strata mapped. Farther north in Mississippi beds which 

 correspond in stratigraphic position to the lower two-thirds or three-fourths of the Tombigbee 

 as mapped in Lowndes County are included by Hilgard in his Eutaw group, and among these are 

 the sections which he indicated as typical of this division in Mississippi. These beds correspond 

 in age and position to a part of the Eutaw of Smith and Johnson, although in the intervening 

 area in Lowndes County beds of the same age were mapped as Tombigbee. This confusion was 

 due apparently to the fact that Hilgard failed to find in Lowndes County any of the beds of 

 dark clay corresponding in position to those farther north, on the basis of which he seems to 

 have differentiated his Eutaw group. These clays are of a resistant character, and where they 

 occur in stream bluffs form rather conspicuous exposures ; but when the division as a whole is 

 considered they constitute only subordinate lenses of clay in deposits made up in the main of 

 glauconitic sands. Such clay beds, however, occur in Lowndes County, being exposed in the 

 banks of Floating Turtle Creek a short distance east of Columbus. 



Readjustment of the nomenclature. — From the facts brought out in the above discussion it 

 is apparent that a readjustment of the nomenclature as applied by Hilgard to the beds subjacent 

 to the Selma chalk m Mississippi is necessary. The classification of the corresponding deposits 



