162 DALL AND STANLEY-BROWN — APALACHICOLA RIVER GEOLOGY. 



clay, together with small, slightly rounded fragments of quartzose mate- 

 rial, and near their upper surface numerous small, dark colored, very 

 round gravel stones, quite uniform in size, stained with iron and looking 

 like peas or buckshot. The lower part of the clays shows evidences of 

 stratification, thin sheets of harder material still remaining, broken up, 

 apparently in situ, but formerly continuous. Occasionally a small dike 

 of quartzose material may be seen standing in the gravel in its original 

 position. 



Conclusions as to the Geologic Structure and Succession. 



The different portions of the generalized section for the Apalachicola 

 region above the Vicksburg limestone which have actually been observed 

 are shown on the accompanying diagrams, together with a column 

 representing the whole series. The relative thickness of the beds is ac- 

 curately represented in the diagrams, except that in the ideal column 

 the thicker beds are somewhat diminished in order to bring it within the 

 limits of the page. It will be seen on examination that, while the series 

 is not complete in any single section, taken collectively there is no gap 

 outstanding between the beds and, humanly speaking, no room for mis- 

 apprehension as to their position and age. Being variable in thickness 

 at different points, an average thickness has been assumed for the ideal 

 section, except in the case of the Chattahoochee limestone, Avhich has 

 been put at 50 feet, and the Vicksburg at a nominal thickness, owing to 

 exigencies of space. 



To avoid possible confusion the symbols used in the sections *are also 

 employed in the sterographic map accompanying the paper. This map, 

 while aj^proximately accurate in its geographic boundaries, is necessarily 

 highly generalized topographically and is merely a conventional pre- 

 sentation of the relation of the several localities and formations. 



EOCE^'^E. 



Beginning at the base of the column, Professor Pumpelly has shown 

 that the Chattahoochee series rests on an erosion surface of the Vicksburg 

 or Orbitoidal limestone which forms the culmination of the Eocene 

 rocks. We have confirmed this by an examination of the fossils sub- 

 mitted by Professor Pumpelly, who also considers that the Chattahoochee 

 and Chipola beds in southwestern Georgia attained a thickness of some 

 200 feet, which has been reduced by solution and settlement to a very 

 small fraction of that amount. , , 



MIOCENE. 



Chattahoochee Limestones. — At Aspalaga the Chattahoochee limestones 

 are in evidence to the amount of 50 feet before disappearing below the 



