1220 



GYPSEOUS PRAIMES — VICKSBURG BLUFJ 



111 



alternating with, lignito-gypseous clays entirely similar to those found in the 

 outcrops on the Southern R. I!., east of Brandon. Sandstone similar to this, as 

 well as to the Fort Adams' rock (1[236), is found overlying the calcareous 

 Vioksburg strata near Raleigh, Smith county, and thus generally along the 

 southern line of the Vicksburg Group. But nowhere, except at Batt's Summit, 

 have I found the lignito-gypseous strata overlaid by the marine fossiliferous 

 limestone of that group. On the other hand, the former — or rather the gray 

 gypseous clays resulting from their disintegration, sometimes occupy the surface 

 of the territory, forming "prairies" (whose gray soil and exclusive Black Jack 

 and Post Oak growth along their borders, readily distinguish them from the 

 "black prairies" formed by the calcareous materials of the marine formations); 

 and "salty spots'" where efflorescences of various salts (chiefly sulphates of lime, 

 magnesia, potash and sometimes iron, and chloride of sodium) appear on the 

 surface, often injuring vegetation greatly. It would seem, however, that in 

 some localities either the lower portions of the Vicksburg, or the upper of the 

 Jackson beds, are interstratitied with heavy, gray clays, gypseous or lignito- 

 gypseous, to whieh the greater portion of the gypseous prairies owe their 

 origin (see (H'215, if.) 



220. Localities of iht Vicksburg Oroyp. — The general features of the Vicksburg 

 bluff, which have already been mentioned, are exhibited in the following section 

 I regret that want of space precludes me from giving the detailed section, in 

 which no less than 1' 1 distinct strata, recognizable at most points, are exhibited. 



(Sec. 31.) 

 SECTION OF THE BLUFF AT VICKSBURG, WARREN COUNTY. 



