THE FORAMINIFERA OF THE MINT SPRING CALCAREOUS MARL 

 MEMBER OF THE MARIANNA LIMESTONE. 



By Joseph A. Cushman. 



INTRODUCTION. 



The Mint Spring calcareous marl member of 

 the Marianna limestone, a lower Oligocene 

 series of beds of the Coastal Plain region, was 

 defined by C. Wythe Cooke' as follows: 



The "chimney rock" facies of the Marianna limestone 

 is replaced in western Mississippi by sands and shell marls 

 for which the name Mint Spring calcareous marl is here 

 proposed. The name is derived from Mint Spring Bayou, 

 a small stream entering Centennial Lake just south of the 

 National Cemetery at Vicksburg. The strata to which 

 the name is applied are exposed beneath a waterfall in the 

 lower course of tlie stream. 



Between ^'icksburg and Pearl River the Mint Spring 

 marl occupies the entire interval between the Forest Hill 

 sand and the Glendon limestone, but east of Pearl River 

 it is overlain by a thickening wedge of the Marianna 

 "cliimney rock." It has not been recognized east of 

 Chickasawhay River, on which it is exposed IJ miles 

 northwest of the mouth of Limestone Creek. Other 

 important exposures are along Glass Bayou at \'icksburg 

 and at Haynes Bluff, 14 miles north of Vicksburg, where 

 it is 2.5 feet thick. 



The type station may be taken as U. S. G. S. 

 station 6452, shell and sand bed at foot of high 

 waterfall. Mint Spring Bayou, Vicksburg, 

 Miss.: C. W. Cooke, collector. 



The other stations represented in the collec- 

 tions here described are as follows: 



6451. Same locality as station 64-52; E. N. Lowe and 

 C, W. Cooke, collectors. 



6447, 6448. Foot of a high waterfall in Glass Bayou, 

 near Vicksburg, Miss. 



6647. Chickasawhay River IJ miles northwest of Lime- 

 stone Creek, 4 miles northwest of Waynesboro, and 1} 



1 Washington Acad. Scl. Jour., vol. 8, No. 7, p. 195, 1918. 



miles southwest of Boiee, Wayne County, .Miss.; C. W. 

 Cooke, collector. 



7671. "Brown's Cave," east bluff of Leaf River half a 

 mile above the bridge on Bay Springs-Raleigh road, in 

 sec. 13, T. 2 N., R. 8 E., Smith County, Miss.; C. W. 

 Cooke, collector. 



The distribution of the species at these 

 stations and of those species which also occur 

 in the younger Byram calcareous marl at its 

 type station is indicated in the accompanying 

 table. 



As noted in my paper on the Byram marl,' 

 many of the species are closely related to those 

 now found living in the Indo-Pacific region. 

 An added example of this relation is SpiriJKna 

 limhata H. B. Brady var. hipnnctata Cushman, 

 n. var., which is a variety in the Mint Spring 

 marl of a species that is characteristic of the 

 Indo-Pacific. 



The fauna evidently represents more than a 

 shoal-water deposit, as it lacks certain of the 

 genera present in the Byram marl which indi- 

 cate shallow water and has a greater abundance 

 of species which indicate deeper water. The 

 occurrence of numerous Lagenidae indicates a 

 depth of perhaps 50 fathoms, and the lack of 

 such genera as Hcterostef/ina, Opercnlina, and 

 Amphifitegiiia indicates a depth of more than 

 20 or 30 fathoms. This statement is based 

 on data obtained from a study of Foraminifera 

 in the Tortugas region in the Gulf of Mexico as 

 well as of their distribution in the Philippine 

 region. 



A systematic treatment of the species follows. 



= U. S, Geol. Survey Prot. Paper 129-E, 1922, 



123 



