Bainhridge, Ga., and of Alum Bluff, Fla. 249 



chee formations eastward ; and the Oak Grove horizon should 

 correspond to the Chesapeake horizon of Alum Bluff at least 

 to the extent of representing the later Miocene of this area. 



Mr. Johnson in his letter mentions only Euchee Ana in 

 Walton Co., Florida, as a more eastern phytogene locality. 

 The connection between the Roberts phytogene locality and 

 the Alum Bluff bed is therefore not determined by as frequent 

 intermediate localities of that description, as could be desired. 

 The better known course of the upper or Chesapeake Miocene 

 must be therefore relied upon (in addition to the correlation 

 evidence just given) to establish the continuity of the lower 

 horizons."* 



The difficulties which are at present being found to distin- 

 guish between the horizons of the more western Miocene 

 localities will be better understood if the effects of two such 

 different currents as the Chipola and the Chesapeake currents 

 are considered. During the deposition of the Chattahoochee 

 along the Appalachicola embayment, the southern current 

 does not seem to have brought in as yet a great quantity of 

 southern or Chipola types. From the nature of this current 

 the fauna would be introduced into this embayment from the 

 west, and in the western losalities an intermixture of Chatta- 

 hoochee and Chipola fossils might occur, while a more rapid 

 introduction of the Chipola fauna at some later date into the 

 Appalachicola region would make the change there more sud- 

 den, and the two faunas would be more distinct in this eastern 

 embayment. At Alum Bluff the later history of the Chipola 

 is that of a formation containing chiefly phytogene remains. 

 During this later period of the Chipola the Chesapeake fauna 

 was being introduced from the northeast, but owing to the 

 phytogene phase at Alum Bluff the intermixture of Chipola 

 and Chesapeake fossils is not shown here, and by the time that 

 marine waters again covered Alum Bluff the southern fauna 

 had been excluded by the Chesapeake current. Towards the 

 west, however, this transformation of faunas may not have 

 been so complete at the close of the phytogene phase, in fact 



* The difference between the correlation here attempted and that suggested 

 by Mr. Johnson, in his paper on the Miocene group of Alabama, loc cit., is that 

 the Alum Bluff plant containing deposits being considered at that time of post- 

 Chesapeake age. it was necessary on the basis of any true principles of correla- 

 tion to classify the phytogene deposits of Alabama, if at all, as post-Chesapeake, 

 instead of pre-Chesapeake, hence Mr. Johnson's desire to classify the fossiliferous 

 deposits at Roberts as the Chesapeake (Alaqua phase) instead of the lowest 

 Miocene, as he informs me Mr. Dall interprets the same. A marginal pencil 

 note by Mr. Johnson to this passage adds '• mixed with some of older time of 

 Chipola " fossils suggesting the possibility that Chipola as well as Chattahoochee 

 fossils may be present below the phj'togeue deposits of Alabama. On the basis 

 of present views the true Chesapeake deposits of Alabama must be expected 

 above instead of below the Hattiesburg phytogene phase. How far these views 

 are correct will have to be shown by future studies. 



