158 DALL AND STANLEY-BROWN — APALACHICOLA RIVER GEOLOGY. 



the north, at a point (C of figure 2) near the camp, the Chesapeake is 

 thinned to 5 or 6 feet in thickness. 



Numbers 6 and 7. — The Chipola marl is compact and of a dark- 

 reddish color from hydrated peroxide of iron contained in it. The 

 fossils which are abundant are rather soft. Orthaulax is the most com- 

 mon shell ; there are no traces of Orbitolites. The matrix is chiefly sand 

 mixed with clay. At least 6 or 8 feet of the Chipola is below the water ; 

 it rises at the lowest stage of the river from 3 to 11 feet above the water's 

 edge, weathering almost like a rock. There is no well defined line of 

 separation between the marl and the Alum Bluff sands (number 6) 

 above it, but the change takes place in a space of 5 feet, the lower por- 

 tion of the sands containing more or less of the Chipola fauna. Above 

 this they are mottled bright ferruginous and 3^ellow, and exhibit distinct 

 marks of cross bedding. They contain sheets — laminse or lenticular 

 streaks of clay — which show^ abundant leaf remains resembling willows 

 and other water-loving plants, while the sands in the loAver part of the 

 bed contain large leaves and stalks of palmetto or other palm-like vege- 

 tation, the thicker parts of which are reduced to the condition of lignite. 

 These are too friable to remove without previous hardening applied in 

 situ. The upper part of these sands did not show any fossil remains at 

 the points where we examined them. 



Toward the north ((7 of figure 2), where the blufi" is much lower and 

 the Chesapeake thinned out to 5 or 6 feet in thickness, the sands below 

 it are unfossiliferous and modified. The upper part is more exclusivelj'' 

 sandy, and, lower down, the bed assumes the clayey compact greenish 

 color of the oyster marl at Rock bluff, a few miles above, but here the 

 green marl contained no fossils. 



Jacksons Bluff and Section. — In this connection, as confirming the iden- 

 tity of age and position of the greenish marl, a section taken by Mr E. 

 Jussen, of the United jStates Geological Survey, may be cited. This sec- 

 tion was made at Jacksons bluff, situated in township 1 south, range 4 

 west, section 17, on the Ochlockonee river, Florida, being about twent}^- 

 one miles east and six miles south of Alum bluff". 



Section at Jacksons Bluff. 



Superficial sands 5 feet. 



Chesapeake bluish marl, with Mactra congesta 8 " 



Gray marly bed, with oysters and Pecten 22 " 



Total thickness. ... '. ... 3^" 



Bristol — From Alum bluff we descended the river to Bristol and 

 Blountstown, the former a landing on the left bank in township 1 north, 

 range 8 west, section 36, with the village of the same name about a mile 

 inland from the river bank. At the landing alluvium and clayey beds 



