UPPER CRETACEOUS. 655 



sion 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 cor- 

 respond to the Tuscaloosa formation but, as previously stated, represent a part of the north- 

 ward extension of the Tombigbee division as mapped and hence correspond in stratigraphic 

 position to a part of the Eutaw of Smith and Johnson. 



The essential difference between the Tuscaloosa and Eutaw divisions of Smith and Johnson 

 may perhaps best be stated as foUows. The Tuscaloosa consists of a series of sands, clays, and 

 gravels in large part of shallow-water origin, characterized by irregularity of bedding and, where 

 the conditions for their preservation were favorable, by the presence of fossil leaves. The Eutaw 

 consists predominantly of glauconitic sand of marine origin which in approximately the lower 

 two-thirds or three-fourths of its thickness contains subordinate lenses of dark clay and exhibits 

 fine cross-bedding and in its upper one-third or one-fourth is made up of massive beds of glau- 

 conitic sand with calcareous sand beds in its upper part. 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 litho 

 logic line of separation between them, the change from the one Idnd of sedimentation to the 

 other having been transitional. 



Beds representing the Tuscaloosa formation extend from western Alabama northward, 

 occurring in a wide belt that includes the northwestern part of Alabama and a relatively nar- 

 row area in the adjoining northeastern part of Mississippi. The formation as a whole, how- 

 ever, becomes much thinner toward the north and disappears in the vicinity of the Tennessee 

 State line. It is doubtful if, in the region of their outcrop, the Mississippi representatives of the 

 division exceed a maximum thickness of 400 feet. Hilgard did not differentiate these lower beds 

 of shallow-water origin from the higher beds of marine origin but included them in his Eutaw 

 fermation, as shown by the map accompanying his report. 



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

 previously stated, aU 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 Ala- 

 bama line is 15 or 18 miles, corresponding to a thickness of 400 or 500 feet, the actual sections 

 given by biTn 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 

 correspond in age and position to a part of the Eutaw division 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, upon the basis of 

 which he seems to have differentiated his Eutaw group. These clays are of a resistant charac- 

 ter and where they occur in stream bluffs form rather conspicuous exposures; but when the 

 division as a whole is considered they constitute subordinate lenses only of deposits made up in 

 the main of glauconitic sands. Such clay beds, however, do occur in Lowndes County, being 

 exposed in the banks of Floating Turtle Creek a short distance east of Columbus. 



From the facts brought out in the above discussion it is apparent that a readjustment of 

 the nomenclature as apphed by Hilgard to the beds subjacent to the Sehna chalk in Mississippi 

 is necessary. The classification of the corresponding deposits in Alabama by Smith and Johnson 

 is based on essential physical differences, namely, those depending on origin. In Mississippi 

 these differences were not recognized. It would appear, therefore, that the Alabama nomencla- 

 ture is the more logical. For this reason, in the opinion of the writer, the name Tuscaloosa, 

 which stands for the lower shallow-water portion of the series, should be extended to include the 

 corresponding deposits in Mississippi. The name Eutaw, which in Alabama stands for the upper 

 or marine portion of the series, can appropriately be extended to include the corresponding beds 



