385 The Oligocene of the Southern United States 75 



150 feet. The sandstones were first named by Wailes^^ from the 

 bluff at Grand Gulf, of which a photograph is shown on the oppo- 

 site page, where they are typical. Later they were described by 

 Dr. Hilgardf as composed of coarse grains of pellucid quartz im- 

 bedded in a mass of opaque white silex. The formation contains 

 gypsum and magnesium salts. The Grand Gulf sandstones are 

 chiefly exposed along the Pearl River and tributaries of the 

 Mississippi. Elsewhere they are likely to be obscured with La- 

 fayette sands. 



Helix 



Loess ^^^g^^ 

 Kimlchen 



Sandy cla^sir^^s 

 Sandstone 



Pebbles ,, . •*~^, 

 Coarse wbih. ' ^^ 



Cross-bedded :^ 



friable sandstone I 



Sands and clay 



Sandstone 

 Clay 



Sandstone 

 Greenish sandy clays 



Section at Grand Gulf. 



1854, p. 216. 



* A^ri. and Geol. 0/ Miss., ist rep 

 ^ Ccol. 0/ 3liss., i860. 



