! a '2l(>, 217, 218 



216. I have also obtained crystals of selenite from Scott county, where, from 

 all accounts, the gypseous prairies are well developed. In Smith county also, 

 N. of Raleigh, at L. E. Crook's place on the Okahay, there is a body oi gypseous 

 and black prairie intermingled, precisely as we find it at John Parker's. It 

 might appear at lust sight that these gypseous strata could be referred to the 

 Grand Gulf Group, and such was my first impression. But it is difficult to 

 reconcile this supposition with their geographical and hypsometrical distribution, 

 besides which, their lithological character is entirely different from the blue or 

 brown laminated claysof the lignuo-gypseous strata which unequivocally overlie 

 the Vicksburg strata, and form "salty spots" in the soil, but nowhere so far as 

 1 have seen, anything resembling the gypseous prairie. On the other hand the 

 clay found in the outcrop on the Peelahatchie is undistinguishable from specimens 

 of the calcareo-gypseous matrix of the Zeuglodon in Mrs. Nichols' field. In 

 Wayne county, too, on the Chickasawhay, heavy, greenish or bluish clays 

 intervene between the Jackson and Vicksburg strata, and everywhere we find 

 intervening between the black prairie territory of the two groups, either the 

 gypseous, or "hogbed prairie" soils. 



The absence, thus far, of deep wells or borings on the territory occupied by 

 the Vicksburg Group and by these doubtful clays, has prevented me from 

 obtaining satisfactory evidence on this question. If, as I suppose, the material of 

 the gypseous prairies is derived from an irregular stratum intervening between 

 the Jackson and Vicksburg Group, it is nevertheless true that in some localities 

 the soils derived from the strata overlying the latter, approach very closely, both 

 in space and quality, to those derived from the lower stratum in question. 



IV. THE VICKSBURG GROUP. 



217. This interesting group, the highest of the marine eocene 

 formation of Mississippi, and the only one which reaches the banks 

 of the Mississippi River (at Vicksburg, where it was first studied 

 by Conrad) occupies a narrow belt of nearly uniform width, south- 

 ward of the territory of the Jackson Group, extending accross the 

 whole of the State, to the Alabama line, and thence to the 

 Tombigbee River, where it forms the well-known bluff at St. 

 Stephens. It is the only one of the marine stages of the eocene, 

 which exhibits crystalline limestones ; associated, however, Avith 

 blue and white marls more or less indurate at times, as is the case 

 with the other groups. 



The marls, which have a tendency to be sandy rather than clayey, are 

 the prevalent materials of the formation, and the chief repositories of the beautiful 

 fossils of the group ; they usually alternate with ledges of blue (or by oxidation 

 yellowish) limestone, more or less sandy and glauconitic, and not unfrequently 

 contain within their mass, indurate, rounded nodules, often very rich in fossils. 



218. It would be difficult, however, to give a description of these calcareous 

 strata without referring at the same time, to the ligni to-gypseous* strata which 

 generally accompany, usually overlie it, and might be considered as strictly 

 belonging to the Grand Gulf Group, but for their being found in one locality at 

 least, overlaid by a string of limestone nodules containing the characteristic 

 fossil of the Vicksburg Group — the Orbitoides Mantelli. Through this, so close 

 a connection is apparently established between the two groups just mentioned, 

 as to afford a strong presumption in favor of the eocene age of the Grand Gulf 

 Group itself. This circumstance, together with the occurrence of tree palms in 



.. clays or sands containing more or less gypsum and lignitic matters. 



