514 PROCEEDINGS OF THE ACADEMY OF [Sept., 



facts, there are several broad and striking differences between the 

 two faunas, such, for example, as the great abundance of Bryozoa 

 in the Jackson and the insignificant representation of this great 

 class of animal life in the Vicksburg. 



Because of the existence of most of these Eocene forms in the 

 Red Bluff bed, I am inclined to consider that horizon more 

 closely related to the Jackson than to the Vicksburg, in spite of 

 the greater' proportion of its species which have been identified 

 with the Vicksburgian. It is possible, also, that many of these 

 supposedly identical forms may prove to be more or less well 

 marked subspecies, and not exactly the same as their Vicksburgian 

 successors. However, not having visited the Red Bluff deposit as 

 yet, it would be unreasonable to pass any definite opinion on this 

 point. 



If my memory serves, Mr. Vaughan informed me some time 

 ago that he had found Alveiniis minutus at Claiborne, Alabama. 

 This species literally swarmed throughout the Jackson stage, and, 

 in fact, is one of the most characteristic upper Eocene species, but 

 no trace of it or of any allied species has occurred in either hori- 

 zon at Vicksburg, even upon diligent special search on the part of 

 the writer and careful washing of considerable quantities of marl 

 from various parts of the beds. The discovery of a species of 

 this genus in the Oligocene of Floi'ida by Dr. Dall is therefore 

 the more surprising. 



As a broad statement, therefore, it may be said that the diver- 

 gence of the Jackson and Vicksburg faunas is so radical as to 

 abundantly justify the assignment of them to different epochs of 

 the Tertiary — the Eocene and the Oligocene. 



It is here necessary to discuss the distribution in time of the two 

 species, Orbitoides mantelli and Pecten poulsoni, before alluding 

 to the White Limestone of Alabama, for these two species seem to 

 have been regarded, especially by Hilgard, as the conclusive ear- 

 marks of the Vicksburg formation. This is an error which has 

 caused much misapi^rehensiou, for there is abundant testimony to 

 prove that they both persist through such an extended range in 

 time as to deprive them of any such value. 



As for Orbitoides mantelli, I personally collected in two partial 

 days at Moody's Branch, and a portion of a day al Montgomery, 

 La., with subsequent washing of a little marl, seventeen speci- 



