206 D. W. Langdon— Tertiary of 



Ostrea Mortonii Gabb, and Zeuglodon vertebra, while the latter 

 is recognized by the crystalline character of its limestone, as 

 well as by its fossils, Pecten Poulsoni Mort. and Orbitoides 

 Mantelli Mort. In Alabama this prairie soil invariably occurs 

 north of these limesinks, and as a southern dip is everywhere 

 recognized the natural inference is that the strata forming the 

 prairie soils should underlie or be older than those forming the 

 limesinks. I have observed these prairie soils in Clarke Co., 

 Mississippi, near Shubuta, and east of that point crossing over 

 into Alabama north of the boundary of Choctaw and Wash- 

 ington Counties. They continue from the Alabama line on- 

 ward into north Washington County, to between St. Stephens 

 and the line of Choctaw County. From this point they can be 

 traced across Clarke County, always occurring north of the 

 "limesink country," into Monroe County where the writer's 

 investigations terminated. 



At St. Stephen's Bluff on the Tombigbee River we have 

 the following section : 



1. Soft white limestone, the upper part containing num- 



bers of Orbitoides Mantelli Mort., Pecten Poulsoni 

 Mort., and a few iScutella Rogersi Mort., all of which 

 become less frequent in the lower 20 feet, the litho- 

 logical character remaining the same 75 feet. 



2. Indurated ledge of blue argillaceous limestone con- 



taining Ostrea eversa Mellv. and large Spondylus 

 damosus Mort. on the under side of the ledge. Some 

 of these Spondyli measure 3" X -¥ 6 feet. 



3. Calcareous clay holding a few obscure fossils, mainly 



bivalves 4 feet. 



4. Yellow glauconitic marl containing nodules of phos- 



phate of lime and some few phosphatic casts — a 

 Comes, several madrepores and Ostrea Mortoni Gabb, 15 feet. 



This section was made at the old Spanish powder magazine. 

 About a half mile below, at the steamboat landing, No. 4 sinks 

 out of view showing a southern dip. 



West of this bluff and at a greater elevation, the limestone 

 becomes crystalline and shows in weathered masses above the 

 surface in the Cedar grove covering the old town of St. Stephens, 

 where the inhabitants call it "horse-bone" rock. 



The Claiborne Ferruginous Sands (Smith) seem to become 

 lignitic as we go west ; for thirteen miles west of Bladon Springs, 

 Choctaw County, the following section is exposed : 



Surface soil and drift pebbles 3 feet. 



1. Limestone somewhat argillaceous, — contains one or 



two hard ledges a foot or two thick — forms prairie 



soils — no fossils seen _ 40 feet. 



2. Indurated limestone ledge full of fossil casts 2 feet. 



