168 BALL AND STANLEY-BROWN — APALACHICOLA RIVER GEOLOGY. 



are prominent species and Mactra congesta the most abundant fossil. 

 The color of the bed and of the fossils in the bed is exactly like that of 

 the Maryland beds of the same age, their cold gray and chalky white 

 color contrasting vividly with the yellow and ferruginous tints of the 

 old Miocene marl and its fossils. 



This bed has been recognized lying upon the Alum bluff beds at Jack- 

 sons bluffj Ochlockonee river (Jussen), and beloAv the Lafayette or red 

 beds and the aluminous clay at Abes spring and Darlings slide. It also 

 occurs near Tallahassee and is reported on Johnson's authority from De 

 Funiak springs. It is probable that this fauna, which has been shown 

 by Dall and Harris* to have penetrated into the gulf of Mexico by the 

 strait named by them the Suwannee strait,t never extended westward 

 of the Mississippi embayment, the synchronous fauna on the Texan 

 side of that gulf partaking much more strongly of subtropical and Pa- 

 cific coast elements. It would not be surprising if, as suggested by 

 Foerste, a mingling of the earlier Chesapeake and latest Chipola species 

 were found to occur at some point on the Gulf coast. But it must be 

 distinctly understood that no reliable evidence of such a mingling, as 

 distinguished from an accidental mechanical mixture of fossils of dif- 

 ferent ages, has yet been shown to exist anywhere. The Oak Grove 

 fossils authorize the inquiry, but cannot as yet offer any proof of such a 

 mixture. The locality would be worth examination by any trained ob- 

 server who would take the time and trouble to definitely ascertain the 

 exact facts, which are not yet at our disposal. 



The Chesapeake marl reaches 7 feet above the water at Abes springs. 

 At Darlings slide there is uncertainty as to its exact thickness, but at 

 neither place is its base discernible or any subjacent rock visible. At 

 Jacksons bluff it is 8 feet thick. 



The Aluminous Clay. — Above the Chesapeake marl at Alum bluff is a 

 bed of grayish glay, apparently more pervious than the marl, as water 

 issues from it all along its face, and, trickling down, leaves an efflores- 

 cence on the surface, from which the bluff derives its name. This clay 

 is 24 feet thick, and was termed " lignitic " by Langdon and Johnson, 

 but contains extremely little vegetable matter, as Foerste pointed out.J 

 We found evidences of fossils, too much dissolved to identify, in this 

 clay, and Mr Foerste states that he found Chesapeake species in it, but 

 does not mention which species. It is highly probable that the clay is 

 of Chesapeake age, and, as it exactl}^ resembles the so-called Pascagoula 

 clay of Vernal, Mississippi, which contains at least one Chesapeake spe- 



* Bull. 84, U. S. Geol. Survey, 1891. 



t Op. cit., p. Ill ; the name of Okeefinokee has since been applied to it by Foerste (Am. Jour. Sci., 

 vol. 46, October, 1893, p. 245), who doubtless overlooked the fact that it had previously been named. 

 X Op. cit., p. 250. 



