THE BYRAM CALCAREOUS MARL OF MISSISSIPPL 



By C. Wythe Cooke. 



HISTORICAL INTRODUCTION. 



The beautiful and well-pi-eserved shells con- 

 tained in the lower Oligocene deposits at Vicks- 

 burg, Miss., early attracted the attention of 

 collectors. Lesueur appears to have been the 

 first to depict them, and the set of five plates 

 engraved by him in 1829 shows a number of 

 the species at Vicksburg. However, as his 

 plates were not accompanied by names or de- 

 scriptions, all the Vicksburg species date from 

 later authors. His name, although not at- 

 tached to any of the species as author, is per- 

 petuated by Scapharca lesueuri Dall, one of 

 the most common and most characteristic mol- 

 lusks of the Byram marl. Conrad, the Nestor 

 of American Tertiary paleontologists, in 1S4.S ' 

 described and figured a large number of fossil 

 mollusks from Vicksburg. Since that time many 

 collectors have visited Vicksburg, and speci- 

 mens from the marls are contained in many 

 cabinets, but no one has attempted a systematic 

 study of the fossils. 



Nearly every student of the Vicksburg beds 

 has recognized a twofold or a tlu-eefold division 

 of the group. Conrad collected chiefly from 

 the topmost marls, but that he was aware of 

 the presence of a lower shell bed and tliat five 

 of his species came from it is plainly stated on 

 pages 207-208 of the volume cited. Hilgurd, in 

 his monumental work on the geology of Missis- 

 sippi,- published a characteristic section of the 

 bluff at Vicksburg but did not propose names 

 for the various beds. Otlo Meyer'' in ISSo 

 distinguished three members of the Vicksburg, 

 for which he proposed the names "Higher 

 Vicksburgian," "Middle Vicksburgian," and 



1 Conrad, T. A., Observations on the Eocene formation and descrip- 

 tions of 105 new fossils of that period from the vicinity of Vicksburg, 

 Miss.: Acad. Nat. Scl. Pliiladolpliia Jour.. 2d ser., vol. I, pp. 111-134, 

 184S; Descriptions of new fossil and recent shells of the I'nited States: 

 Idem, pp. 207-209, 1S49. 



• Hilgard, E. W., Report on the geolog.v and agriculture of the State 

 of Mississippi, p. 141, 1860. 



"Meyer, Otto, The genealogy and the age of the species in the southern 

 Old Tertiary, pt. 2: Am. Jour. Sci., 2d ser., vol. 30, p. 71, 188.5. 



"Lower Vicksburgian." The middle and lower 

 divisions of Meyer constitute but one horizon, 

 in the opinion of Casey,'' who says: 



At Vicksburg there are two distinct horizons. » * * 

 The lower Vicksburgian consists of alternate thin strata 

 of gray sands, sandy clays, and varialily but usually loosely 

 compacted white or gray limestone. The upper consists 

 of a much thinner bed of more or less red-brown mail, 

 often indurated into nodular mas,seR or subindurated, and 

 without trace of limestone, having rarely, however, thin 

 layers of glauconitic sand.s and comminuted shells, in 

 which entire sjiecimens when found are generally much 

 distorted by pressure. The faunas of these two beds 

 differ very markedly. 



In 1918 I proposed names for the several 

 formations of the Vicksburg group ^ and drew 

 up the correlation table shown on page 80. 

 The detailed evidence upon which this correla- 

 tion is based is still awaiting publication. 



The present paper is designed to describe 

 briefly the youngest formation of the Vicks- 

 burg group, the Byram marl, to give an account 

 of its more notable exposures in Mississippi, 

 and to enumerate some of the fossil species 

 that have been found in it. The formation 

 is more fully described in a manuscript by me 

 awaiting publication by the Mississippi State 

 Geological Survey. I hope before long to 

 undertake the systematic description of the 

 mollusks of the Vicksburg group. 



GENERAL FEATURES. 



The topmost formation of the Vicksburg 

 group, the Byram calcareous marl, is named 

 from the village of Byram, on Pearl River, 

 Miss., about 9 miles below Jackson. The 

 Byram l)eds were supposed by Casey" to con- 

 stitute a "substage" intermediate in age be- 

 tween the Red Bluff clay and the Mmt Spring 

 marl, but more detailed study of the mollusks 



* Casey, T. L., On the probable age of the .\Iabama white limestone: 

 .\cad. Nat. Sci. Philadelphia Troc, vol. 53, p. 515, liioi. 



■' Cooke, C. W., Correlation of the deposits of Jackson and Vicksburg 

 ages in Mississippi and .\laV»ama: Washington Acad. Sci. Jour., vol. 8, 

 p. 187, 1918. 



•Op. cit., pp. 517-518. 



79 



