26 CRETACEOUS DEPOSITS OF THE EASTERN GULF REGION. 



from this basal horizon to the successively higher horizons the number of common species 

 diminishes. (2) Although showing this relationship the fauna contains elements distinct from 

 anything known at higher horizons. (3) It bears about the same relationship to the invertebrate 

 fauna present in the upper part of the Black Creek formation of the Carolinas that it does to 

 the fauna of the basal beds of the Ripley formation (part of Exogyra ponderosa zone between 

 the Mortoniceras subzone and the Exogyra costata zone) in the Chattahoochee region. The 

 basal beds of the Eutaw formation are therefore stratigraphically lower than the invertebrate- 

 bearing beds of the Black Creek formation and, in the opinion of the writer, correspond approxi- 

 mately to basal noninvertebrate-bearing beds of that formation. (4) The basal beds of the 

 Eutaw are represented at Charleston, S. C, by beds penetrated in a well boring between the 

 depths 1,974 and 2,007 feet, which in turn probably represent the basal beds of the Black Creek 

 formation of the Carolinas. (5) The actual evidence for a comparison of the basal Eutaw 

 fauna with the Cretaceous faunas of Xew Jersey is slight, but combined with evidence furnished 

 by the faunas from overlying horizons there seems to be sufficient grounds for correlating the 

 containing strata approximately with the Magothy formation. 



To the west, in Alabama and Mississippi, the invertebrate-bearing basal beds of the Eutaw 

 of the Chattahoochee region are represented by corresponding basal Eutaw strata in which no 

 well-preserved invertebrates have as yet been discovered. 



Plants. — Fossil plants have been obtained at several horizons in that part of the Eutaw 

 formation below the Tombigbee sand member (Mortoniceras subzone). E. W. Berry, who 

 studied them, recognized 27 species. He gives the following statement of his views on the 

 significance of the plant remains in correlation : 1 



It is clear that the flora of the Eutaw formation of Georgia is of approximately the same age as the Magothy- 

 Matawan flora of the northern Coastal Plain and the Black Creek flora of the Carolinas. It has much in common 

 with the much more extensive Tuscaloosa flora of western Alabama, but is probably younger than the bulk of the 

 Tuscaloosa flora or that found in the Middendorf arkose member of the Black Creek formation. 



The evidence furnished by the plants as interpreted by Berry is in essential agreement with 

 that afforded by the invertebrates. 



The Coffee sand member of the Eutaw formation, which is believed to be included within 

 the part of the Exogyra ponderosa zone above the Mortoniceras subzone, lias yielded the species 

 Sali.r eutawensis Berry. This species was found by the writer in a cut of the Nashville, Chat- 

 tanooga & St. Lmiis Radway a short distance east of the station at Parsons, Decatur County, 

 Tonn., and was identified by Berry. This form occurs in the extreme basal beds of the Eutaw 

 formation at Broken Arrow Bend on Chattahoochee River and in the Black Creek formation 

 of Xorth Carolina, which indicates that the species ranges from the base of the Eutaw formation 

 well up into the Exogyra ponderosa zone. The presence of the species in the Coffee sand tends 

 to confirm tin- reference of this division to a position below the Exogyra costata zone; it can not, 

 however, be taken as indicating any particular horizon between the base of the Eutaw formation 

 and the to]) of the Exogyra ponderosa zone. 



Vertebrates. — The following vertebrate species, all sharks, have been collected from beds near 

 the base of the Etitaw formation at Broken Arrow Bend: Coraxfalcatus Agassiz, Lamna Uxana 

 Roemer, Otodus appendiculatus Agassiz. As these species are all known to have a wide strati- 

 graphic range they have no value in close correlation. 



EXOGYRA PONDEROSA ZONE. 3 



RANGE OF THE SPECIES. 



The species Exogyra ponderosa Roemer makes its first appearance near the base of the 

 Tombigbee sand member of the Eutaw formation and ranges up to about the middle of the Sehna 

 chalk and its corresponding nonchalky equivalents. The lower boundary of this zone is shown in 

 Plates IX and X by the red letter P and the upper boundary by the red line 2. The restriction of 

 the species in stratigraphic range and its broad geographic distribution within the limits of its 



> Berry. E. W., The Upper Cretaceous and Eocene floras of South Carolina and Georgia: Prof. Paper C S. Geol. Survey No. 84 (in press). 

 = See pp. 41-50. 



