198 COOKE : JACKSON AND VICKSBURG DEPOSITS 



In western Mississippi the close of Jackson time was followed 

 by shoaling of the sea, attended by a southward recession of 

 the strand line, in the course of which the lignitic beds and 

 laminated' and crossbedded sands of the Forest Hill were de- 

 posited. In eastern Mississippi and Alnbama, however, the 

 change from Eocene to Oligocene time was not accompanied by 

 changes in physical conditions affecting materially the character 

 of the sediments, for the clay of the upper Jackson and the 

 limestones of the Ocala are succeeded by similar materials in the 

 Red Bluff clay and the Marianna limestone. 



While the lignites and crossbedded sands of the Forest Hill 

 were forming in the west and the marine clays and marls of the 

 Red Bluff were being deposited in the intermediate region, the 

 calcareous sediments of the Marianna limestone were accumu- 

 lating on the Floridian plateau and adjacent parts of Georgia 

 and Alabama. As time went on the phase of deposition produc- 

 ing ''chimney rock" progressed westward, and the Marianna 

 limestone overlapped first the Red Bluffs beds and then part of 

 the Mint Spring marl until it had reached the ninetieth meridian. 

 Subsequently, nearly uniform conditions, attending the deposi- 

 tion of the Glendon limestone, prevailed across Mississippi and 

 far into Alabama. Therefore, the Marianna limestone repre- 

 sents a longer time interval in the east, where it includes both 

 the middle and the lower Vicksburg, than in the west, where it is 

 restricted to the middle Vicksburg. 



Deposition of the Byram marl appears to have succeeded 

 without interruption that of the Glendon limestone, but the 

 change in character of the sediments indicates a more plentiful 

 supply of mud and sand. 



The stratigrapjiic relations of the Byram marl to the overlying 

 Catahoula sandstone are conjectural. At none of the places 

 where the contact of the two formations has been seen, has any 

 indubitable evidence of unconformity been observed, but at 

 some localities, as near Waynesboro, Mississippi, the change in 

 lithology is so abrupt as to suggest the probability of an inter- 

 ruption in deposition. At other places the transition is so 

 gradual that deposition appears to have been continuous. 



