CRETACEOUS-EOCENE CONTACT 

 TOMBIGBEE RIVER, ALABAMA 



EUGENE ALLEN SMITH 



University, Ala. 



The Selma chalk, which is so beautifully exposed at Demopolis 

 on the Tombigbee River, grades upward into a more argillaceous 

 material a few miles below the town. A fine exposure of this variety 

 is at Barton's Bluff on the left bank of the river, about ten miles 

 below Demopolis. For a distance of a mile or two above Barton's 

 and at the bluff itself, there are scores of faults of a few feet dis- 

 placement. Some of these are of the nature of step faults, others, 

 especially as the bluff is neared, bring the white chalk of the Demop- 

 olis variety in wedge-shaped blocks up into the dark-colored clayey 

 material characteristic of the bluff as a whole. In places the strata 

 show a very considerable amount of flexure in addition to the faulting. 

 Fig. I is given in illustration. 



Below Barton's for some distance the banks of the river show 

 very few good sections until Moscow Landing is reached. Here the 

 bent, fractured, and faulted beds of the Cretaceous are overlain 

 unconformably by the lowermost (Midway) beds of the Eocene of 

 this section. 



The main mass of the Cretaceous, forming the base of the sec- 

 tion exposed at Moscow, is a light-colored argillaceous limestone 

 not unlike the Selma chalk of the Demopolis type. The dark-colored 

 clayey beds of Barton's Bluff are not shown here. This limestone 

 is a somewhat massive rock with stratification lines very obscure, 

 but near the top of the formation there is a thin layer of phosphatized 

 shell casts which may easily be followed along the bluff and by 

 which the attitude of the strata may clearly be made out. The 

 Eocene beds which form the upper fifteen or twenty feet of this section 

 are of material very similar to the Cretaceous limestone below. Along 

 a good part of the bluff this Eocene limestone lies in immediate 

 contact with the Cretaceous, and when this is the case the uncon- 



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