387 The Oligocene of the Southern United State.s 77 



burg species from the former localitj-, and Dr. Hilgard''^ mentions 

 a ledge of Vicksburg limestone with Orbifoides, Area rnississippi- 

 ensis and PeHen Poidsoni along the Ba3^ou. These outcrops form 

 the western limits of the Vicksburg series. 



Grand Gulf sandstones and clays. The Grand Gulf beds are 

 interrupted by the Mississippi River and its wide alluvial plains, 

 but they reappear at Sicily Islandf and again near Harrisonburg. 

 Passing thence across the state in a southwesterly and westerly 

 direcflion, they enter Texas. A cut through typical Grand Gulf 

 sandstone near lycna is shown in the photograph I on the oppo- 

 site page. 



In the southern portion of the Grand Gulf area, the sand- 

 stones merge into variously colored clays. In this, and in other 

 respe(5ls, these beds present a close similarity to those of the 

 same series in Mississippi. As in that state, the rugged surface 

 topography of the sandstone area forms a marked contrast to the 

 level plains %vhich are underlaid by Vicksburg and Jackson lime- 

 stones. 



Flora and fatina of the Grayid Gulf. The Grand Gulf beds 

 in Louisiana, as in Mississippi, contain wood of dicotyledenous 

 trees and palms, but no animal remains have yet been reported. || 



During the past winter, a bed containing a number of Unio- 

 nidce was found by Prof. Harris at Chalk Hills, two and three- 

 quarters miles south of Rosefield in the southwestern quarter of 

 Sedlion 7. 



Unionidce from Grand Gulf series. The fossiliferous lawyer, 

 which is but five or six inches in thickness, is interstratified with 

 white clays. The latter are popularly called chalk, and have 



* Amer. Jour. Set., vol. 30, 1885, pp. 266-269. 



fSee Darby, Emigrant's Guide, 181S. 



tFrom Geol. Survey Louisiana, Harris and Veatch, 1899, facing p. 96. 



II The scarcity of organic remains was explained by Dr. Hilgard, in 1S71 

 {Amer. Jour. Sci., vol. 2, p. 348), as due to the temporary conversion of the 

 Gulf of Mexico into a dead sea. In 1874, he abandoned this explanation in 

 favor of the theory that the organic remains had been obliterated by the 

 oxidizing influence of ferruginous solutions percolating from above. {Ibid., 

 vol. 7, 1874, pp. 208-210). 



