868 PROCEEDINGS OF THE ACADEMY OF [1880. 



Bluff may be accounted for on the supposition that they have 

 dipped under, whicii would be in harmony with what we know 

 concerning the dip of the beds in this region. This is but locally 

 or at best, but partially indicated in Tuomey's reports, but judg- 

 ing from the contour lines of the cretaceous formation on the 

 general maps appended to the first and second Reports, and from 

 the north and south sections on the map of 1849, as well as from 

 the facts obtained in Mississippi, it must be in a direction west of 

 the southern line, or in other words, S. by W. Dr. Smith has 

 found the loss by dip in a southerly direction on the Tombigbee 

 River to be about 10 feet to the mile, which accords well with . 

 Hilgard's observations on the Upper Eocene and Oligocene forma- 

 tions of Mississippi.^ 



From pala?ontological evidence alone the three exposures in 

 question might readily be taken to represent rather an Upper than 

 a Lower Eocene horizon, for in addition to the species typical of 

 the American Middle Eocene, or Claiborne group proper ( Calca- 

 reous Claiborne of Hilgard), and to the new or undescribed forms, 

 we have the following which have not been hitherto recognized as 

 belonging to the formation, and which, on the contrary, were 

 originally described (at least the majority of them) from deposits 

 of newer date. 



Caricella (Voluta) Bandoni, Deshaye?, sp. {Aniiiian.ic s. Vert'br., lidnKin de P<iiix, 

 II, PI. 1(12, tigs. 13 aud 14), frDiu the " caloaire grossier," Middle Eocene of most 

 geologists, Upper Eocene of Judd. Knighi's Branch. 



Natica Mississippiensis, Cuurad (J. A. X. S. 2d series, i, p. 1 14), originally described 

 from the \'icksburg (<)ligocene) group, but also foind in the .Jackson ( Upper 

 Eocene) deposits. Cave Branch. 



Pleurotoma acuminata, Sowc by (Mineral Conchology, Vol. ii, p. 105), from the 

 London Clay of Highgate (Lower Eocene of most geologists, Middle Eocene of 

 .ludd), and Barton clay (Upper Eocene)? (I have bad no specimens of this species 

 with which to institute direct comparisons, but from a careful examination of 

 Sowerby's and E<lvvards' figures and descriptions there appear to me to be no 

 justifiable grounds for se])arating the species figured on PI. 2(1, tig. 10, from its 

 European ally. Cave Branch. 



Pyrula tricostata, Doshayes (('<><iiiiUm Fosxil «, ii, p. 584), from Retheuil and Uuise- 

 Laraothe, Middle Eccene (Suessonian of d'Orbigny). Cave Branch. 



^ Hilgard fovind the dip of the Jackson and Vicksburg strata to be from 

 10 to 13 feet per mile S. by W., at "points where the great regularity of 

 succession for a considerable distance seemed to indicate a normal config- 

 uration." (A. J. Science, new series, xliii, p. 36.) 



