14 CRETACEOUS DEPOSITS OF THE EASTERN GULF REGION. 



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 nomenclature is the more logical. 



In the opinion of the writer, the name Tuscaloosa, which stands for the lower irregularly 

 bedded portion of the series, or for that portion which originated in shallow water, should be 

 extended to include the corresponding deposits in Mississippi. 



The name Eutaw, which in Alabama stands for the upper or truly marine portion of the 

 series, can appropriately be extended to include the corresponding beds in Mississippi, although 

 this will mean the expansion of the term (as Hilgard used it) to include the Tombigbee sand 

 above and its contraction to exclude the Mississippi representatives of the Tuscaloosa formation 

 below. 



The name Tombigbee sand, however, if applied to the actual type sections of the division 

 given by Hilgard and to their equivalents, is expressive of a natural phase or subdivision of the 

 Eutaw formation and is eminently worthy of preservation in the literature. If Hilgard's imper- 

 fect mapping is disregarded the sections of the Tombigbee sand given by him are all included 

 within a thickness of strata which probably does not exceed 150 or 200 feet. Thus limited, the 

 division includes the uppermost massive, glauconitic, more or less calcareous and phosphatic 

 beds of the Eutaw formation, as distinguished from the more irregularly bedded and more 

 argillaceous portion of the formation beneath it. These upper, massive beds are traceable for 

 many miles northward from Lowndes County, in Mississippi, and with certain modifications they 

 extend eastward entirely across Alabama into Georgia. They were recognized by Smith and 

 Johnson and were spoken of by them as the ''upper member of the Eutaw formation." This 

 member, however, can not be sharply differentiated from the remainder or lower part of the 

 formation, for massive lenses of glauconitic sand of greater or lesser extent occur in places at 

 lower levels than the Tombigbee member proper and in small exposures are not distinguishable 

 from that member. 



The names Tuscaloosa and Eutaw were applied in Mississippi by Crider ' in 1906 in approx- 

 imately the sense here proposed, but he did not give his reasons for discarding the classification 

 of Hilgard in favor of that of Smith and Johnson. 



Extent of the Tuscaloosa formation.- — Beds representing the Tuscaloosa formation extend 

 north from western Alabama in a wide belt, which includes the northwestern part of Alabama 

 and a relatively narrow strip in the adjoining northeastern part of Mississippi. The formation 

 as a whole, however, becomes rapidly thinner to the north and disappears in the vicinity of the 

 Tennessee State line. It is doubtful if in the region of their outcrop the Mississippi representa- 

 tives of the formation exceed a thickness of 400 feet. Hilgard did not differentiate these lower 

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

 his Eutaw formation, as shown by the map accompanying his report. The Tuscaloosa forma- 

 tion also extends from western Alabama eastward nearly to Alabama River, where the terrane 

 is believed to pinch out rather abruptly between the unconformably subjacent Lower Creta- 

 ceous beds and the overlying Eutaw formation. 



Extent of the Eutaw formation. — The Eutaw formation, as defined by Smith and Johnson, 

 including the Tombigbee sand, extends northward through Mississippi without much change in 

 stratigraphic boundaries, as far as northern Itawamba County. Here the upper boundary shifts 

 abruptly to a much higher level, for in this region the basal part of the Selma chalk merges 

 northward into massive marine sands indistinguishable in lithologic character from the typical 

 Tombigbee sand. A tongue of impure, argillaceous, and sandy chalk, however, extends north- 

 ward into the body of the Tombigbee member in eastern Lee County. (See PI. IX, in pocket.) 

 Still farther north in eastern Alcorn and western Tishomingo counties these massive beds merge 

 horizontally into glauconitic marine strata characterized by irregular bedding and by thin 

 lamina? and thinly laminated layers of dark clay. These extend northward as a narrow belt 

 for a distance of 80 or 90 miles into Tennessee. This is the Coffee sand of Safford. 2 



1 Crider, A. F., Geology and mineral resources of Mississippi: Bull. U. S. Geol. Survey Xo. 2S3, 1906, pp. 12-16. 



= Saflbrd, J. M., On the Cretaceous and superior formations of west Tennessee: Am. Jour. Sci., 2d ser., vol. 37, 1861, pp. 360-372; Geology of 

 Tennessee, 1S69, pp. 411-114. 



