Mesozoic and Ccenozoic Geology and Paloiontology, 81 



generall}' highly fossiliferous, and irregular, rounded nodules of iron 

 P3'rites of a radiated structure called "sulphur balls" are common. 

 It is of great thickness on its southwestern border in Chickasaw, 

 Octibbeha, Noxubee and Kemper counties, where borings have been 

 made in it from 700 to 1000 feet, but there is a gradual thinning out 

 northward, through Pontotoc, Itawamba, Tippah and Tishamingo 

 counties to the line of Tennessee. The surface area of this sub- 

 division in Mississippi is greater than that of the other three com- 

 bined. 



The Ripley Group forms the border of the western exposure of the 

 Cretaceous, from a point in Chickasaw through the central part of 

 Pontotoc, the eastern part of Tippah and western part of Tishamingo 

 to th'fe south line of Tennessee. It consists of hard crj'stalline lime- 

 stone, more or less sandy and glauconitic, which forms the highest 

 strata; and bluish micaceous marls, more or less sand}', and often in- 

 terstratified with subordinate ledges of sand}^ limestone, which latter 

 become less and less frequent as we descend in the series toward the 

 strata forming a transition into the Rotten limestone. 



Meek and Hayden* described, from (Fort Benton Group) the mouth 

 of Vermilion river, Ammonites vermiUonensis^ now Mortoniceras ver- 

 nu'lionense ; from near the Black Hills, Scaphites warreni ; from Little 

 Blue river, Inoceramus aviculoides, now I. problematicus, var. avicu- 

 loides ; from (Fox Hills Group), Moreau river, Phylloteuthis subova- 

 tus, Dentalium pauperculum^ now Entalis paupereula, and Cylichna 

 scitula ; from 20 miles below the mouth of Cannon Ball river, Tellina 

 formosa^ now Linear ia formosa ; from ttie north branch of Chej^enne 

 river, Cyprina humilis, now Veniella humilis ; and from Long Lake 

 Avicula subgibbosa, now A. Ungiciforniis, var. subgibbosa ; from the 

 mouth of Judith river (Judith river Group), Helix evansi, now 

 Hyalina evansi; from the mouth of Grand river, Sphcerium planwm^ 

 S. recticardinale, Cyrena cytheriformis, now Corbicula cytheriformis^ 

 and Inoceramus subcompressus, now /. cripsi^ var. subcompressus ; 

 from (Fort Pierre Group), the head of the south branch of Cheyenne 

 River, Helicoceras angulatum^ now Heteroceras angulatum. Ammon- 

 ites placenta^ WHY. inter calar is; now Placenticeras placenta^ var. inter- 

 calaris', from the Yellow Stone river, Scaphites nodosus^ var. jjlenus^ 

 Aporrhais pari-a, now Anchura parva, A. sublaevis, and Mactra 

 gracilis; from Fort Clark, Teredo selUformis ; from White river. 

 Inoceramus vanuxemi, I. balchi; from Bijou Hill, Anomia subirigon- 



'■•' Proc Acad. Nat. Sci- 



