Tennessee River and Crawfish Distribution 



,Ss o Ur / 



Fig. 2. Distribution of western species of Procambarus (Pennides). Arrow as in 

 Figure 1. Solid vertical rulings = P. (Pe.) ablusus; broken vertical rulings = P. 

 (Pe.) lylei; solid horizontal rulings = P. (Pe.) ouachitae; broken horizontal rul- 

 ings = P. (Pe.) clemmeri; cross-hatching = P. (Pe.)penni; stippling = P. (Pe.) la- 

 gniappe; enclosed by open circles (2) = P. (Pe.) elegans. 



"Miocene" belt. Northeast trending fluvial ridges, which form a drain- 

 age divide, readily explain the disparity (Fig. 5). The underlying depos- 

 its that defend the ridges are mapped as Citronelle Formation (Pliocene- 

 Pleistocene). (It should be noted that many geologists question the 

 accuracy of equating the Mississippi-Alabama Citronelle with the for- 

 mation of the same name farther to the east in Florida and to the west 

 in Louisiana.) Brown's analysis of the gravels led him to postulate the 

 existence of a "very large river flowing southwestward" (p. 82), the 

 gravels forming a part of that river's bed. 



New studies, using different and more modern techniques, have 

 helped resolve some of these problems. An important aspect of contem- 

 porary geology, especially along the Gulf Coastal Plain, is the greatly 

 expanded search for fossil fuels. Geologists are no longer confined to 

 outcrops as sources of stratigraphic data. Indeed, the economic consid- 

 erations of the petroleum industry have mandated an intensive study of 

 subsurface formations and expanded drilling activities. The masses of 

 new information have transformed the study of the Coastal Plain into a 

 rapidly evolving, incessantly refined activity. Along with this have come 

 many reevaluations of the relationships between stratigraphic series, 



