516 PROCEEDINGS OF THE ACADEMY OF [Sept., 



of the Vicksburg forms with the species iu question, it will be 

 readily perceived that Peden poulsoni, because of its extended 

 duration in time, is deprived of any decisive value as a criterion. 

 Besides this, however, I find that there are at Vicksburg two well- 

 defined subspecies, or perhaps closely allied distinct species, one 

 characterizing the lower and the other the upper horizon, which 

 have been indiscriminately alluded to as mulsoni for many years; 

 it is quite possible that neither of them is exactly the same as 

 that species, which was apparently described originally from the 

 White Limestone itself. 



On the Tombigbee river, near St. Stephens, and on the Ala- 

 bama river, near Claiborne, there appear more or less conspicuous 

 bluffs composed of a white limestone, which has been designated 

 the Alabama White Limestone. The lower portion of the bluff at 

 St. Stephens has been considered to be Jacksonian, while the 

 upper part, which is apparently a conformable continuation, 

 although differing noticeably in lithological character, has been 

 identified as Vicksburgian, primarily because the limestone here 

 becomes orbitoidal, and, secondarily, because it also contains a 

 few fossils, especially Peden poulsoni, which bear a strong resem- 

 blance to species occurring at Vicksburg. In accepting this as a 

 fact we are forced to admit that two horizons, diftering at least 

 quite as radically in their fauna as any other two consecutive stages 

 of the American Tertiary, are here conformably united in a con- 

 tinuous blufi of limestone. This would seem to be incongruous 

 and highly improbable on general reasoning, but in my opinion it 

 is not a correct statement of the case, and the above discussion of 

 Orbitoides and Peden poulsoni renders it quite unnecessary to form 

 any such conclusion. It seems much more probable that the 

 entire White Limestone of Alabama, including the coral lime- 

 stone, is intermediate in age between the Claiborne and Jackson 

 stages." I feel the more confident in this statement on again con- 



^The examples of Orbitoides coutaiued in a specimen of the White Lime- 

 stone from Clarke conuty, Ala., from the lir.>t bed above the Claiborne 

 sand, which I have before me, ditTer very nuuh from tliose occurring at 

 either Jackson or Vick>biirg in their much larger size; in fact they would 

 almost appear to constitute a distinct species, and in any event they repre- 

 sent the maximum development of the genus in the Southern Tertiary. 

 The Jackson and Vicksburg form is a degradational type derived from the 

 White Limestone, and, as the White Limestone form is the one which was 

 originally published under the name mantelli, it is the Vicksburg niodifica- 



