311] G. E. Dorsey 113 



where glauconitic deposition could take place, does not neces- 

 sarily imply that it lived everywhere where such conditions 

 existed, any more than its isolated occurrence in beds of 

 neither a glauconitic nor a chalky phase proves that the con- 

 stant association with such phases is 'of no significance. The 

 close proximity of the localities in the Carolinas, however, and 

 the evidence in favor of fairly widespread similar conditions 

 during Peedee time point rather to incomplete fossil col- 

 lections than to absence of the form. ' 



Passing to the south, and southwest, the horizon of the 

 Monmouth, marked by greensands thus far, gives way to 

 chalk. The Selma Chalk, the time equivalent of part of the 

 Eipley, is the next source of B. americana. The greatest 

 development of the Selma Chalk is in central and western 

 Alabama, and in east-central Mississippi. To the north in 

 Mississippi the Chalk thins rapidly and becomes very argil- 

 laceous, and in Tennessee is a very thin basal layer of the 

 Eipley formation. An examination of the tables of species 

 prepared by L. W. Stephenson (9, facing p. 24) reveals the 

 widespread occurrence of B. americana in the Selma Chalk. 

 Thus in east central Mississippi and adjacent parts of Ala- 

 bama, it is recorded from 9 localities; in the region of War- 

 rior and Tombigbee rivers, Alabama, from 2 localities; from 

 the vicinity of the Alabama Eiver, Alabama, from 2 locali- 

 ties. About a quarter of a mile east of Troy, Mississippi, an 

 occurrence of B. americana is recorded at about the juncture 

 of the Selma and the Eipley (U. S. G. S. Location 6471) ; 

 and in the northern Mississippi area (N. B. % Sec. 14, T. 

 4 S., E. 5 E., at U. S. G. S. Location 544) the form has been 

 recorded in the Eipley formation ; and there is no record of its 

 occurrence in the Selma Chalk proper in either of these imme- 

 diate regions. Inasmuch as B. americana occurs over this 

 large area, practically everywhere in the Selma Chalk, which 

 " consists in the main of more or less argillaceous and sandy 

 limestones, rendered chalky by their large content of Fora- 

 miniferal remains, with interbedded layers of nearly pure, 



