CHIPOLA MAEL AND ALUM BLUFF BEDS. 165 



The Chattahoochee limestone has been observed above the Vicksburg 

 in southwestern Georgia (Bainbridge, Blue springs, Wileys landing), and 

 in Florida, at the surface or overlaid only by the Lafayette (River Junc- 

 tion \ conformably overlaid by the Chipola marl (McClellan's marl-bed, 

 Chipola river), or by the Alum bluff beds (Old Chattahoochee landing, 

 Aspalaga, Rock bluff). 



Chipola Marl — The Chipola marl which immediatelv overlies the 

 Chattahoochee limestone is a very calcareous mixture of broken shells, 

 fine clay, fossils, and fine sand. When in its normal state it is of a pale 

 yellow, but at Alum bluff is oxidized to a dark red. It is replete with 

 organic remains which are often in a fine state of preservation. More 

 than 400 species have been collected by Burns and the writers, of which 

 only a portion of the Gasteropods have been fully worked out. Orthau- 

 lax gahbl, Strombits aldrichi, Venus kuigdonl, many Cerites and Turritellas, 

 MargineUas and Trochids are among the more conspicuous fossils. There 

 is a remarkable absence of foraminifera and echinoids and the corals are 

 few, mostly small, solitary species. The deposit is one which must have 

 been formed under very favorable conditions of food-suppl}^ and in a 

 dejoth of water greater than that which occurs within the limits of the 

 tides. This explains its absence in tlie sections where the Chattahoochee 

 is covered by beds which were obviously deposited in shallow water, as 

 at Aspalaga, Rock bluff and old Chattahoochee landing. The observed 

 thickness of the Chipola bed does not much exceed 15 feet, but in favor- 

 able localities it may hereafter be shown to have considerably exceeded 

 this amount. 



Alum Bluff Be(h. — At Alum bluff the Chipola marl is conformably 

 overlaid by the deposit named by Dall in 1891 the Alum bluff beds, 

 which there attains a thickness of nearly 22 feet. Tlie change at the 

 point A-B, figure 2, from the marl into the sands is not abrupt, but 

 gradual, and takes place in a depth of about five feet, the fauna of the 

 marl-bed being represented in the sands by quite a number of its species 

 in this transition zone. Above the sands show no fossils or only phyto- 

 gene remains. The composition of the Alum bluff beds is chiefly sand, 

 with a little clay intermixed, and occasional apparently lenticular 

 masses of clay almost pure. The sands are yellowish or pale ; the clay 

 pale gray, both oxidized in streaks, when they are of various shades of 

 ferruginous yellow verging into orange. When the face of the bluff is 

 cleared of weathered material the sands above the lower five or six feet 

 are seen to be clearly and distinctly cross bedded. In the lower por- 

 tion are numerous plant-remains, some of them, apparently palmettos, 

 attaining a very large size and having the woody stems converted into 

 streaks of lignite. The phenomena indicate clearly, as Foerste has 



