CRETACEOUS-EOCENE CONTACT 431 



formity is very little apparent, since the phosphatized shell-cast layer 

 of the Cretaceous, above alluded to, runs practically parallel to the 

 stratification lines of the Midway with a gently undulating dip down 

 stream. Near the base of the Eocene there is a thin layer of shells 

 of a small oyster (O. pulaskensis, Harris) which very clearly indi- 

 cates the attitude of the Eocene strata, as the layer of phosphatized 

 shell casts does that of the Cretaceous. At the extreme right and 

 left of Fig. 2, this approximate conformity is shown. The dark line 

 immediately above the contact is made by the layer of oyster shells. 



Fig. I. — Flexures and faults in. Cretaceous strata at Barton's Bluff, Tombigbee 

 River, ten miles below Demopolis, Ala. 



At intervals, however, especially in the up-stream part of the 

 bluff, there are hollows in the Cretaceous limestone, formed partly 

 by erosion and partly by flexure, in which are plano-convex lens- 

 shaped masses, twenty to forty feet in length, made up (a) of a sort 

 of conglomerate of Cretaceous shells, mainly exogyras and gryphoeas, 

 in a chalky argillaceous limestone matrix, in all some three or four 

 feet in thickness, and above this, (b) a glauconitic sandstone, strongly 

 crossbedded and filled with Cretaceous shells, some of them very 

 much water-worn. These two fillings may clearly be seen in the 

 lens at the left of Fig. 2. In the lens at the right of the figure the 

 sandstone is very prominent, but the underlying shell conglomerate 

 does not show so well. A remarkable thing about these sandstone 

 lenses is the manner in which the strata are flexed and their edges 



