6 Calvin Goodrich 



The Geological Problem 



In Cretaceous times, Georgia from Columbus northward and part of 

 eastern and northern Alabama constituted a peneplain. The line westward 

 from Columbus, Georgia, to Wetumpka and thence northwest through 

 Centerville. Tuscaloosa and Fayetteville was the shore of the gulf which 

 stretched as far as Cairo, Illinois, covered the western thirds of Tennessee 

 and Kentucky, the greater part of Mississippi, part of Arkansas and the 

 whole of what is now Louisiana. A stream of which the Coosa is now 

 an existing part rose south or southeast of Chattanooga and emptied into 

 the sea at or close to Wetumpka. 



C. C. Adams describes the streams of the era in this region as in a con- 

 dition of fine balance. In such a condition slight crustal changes might 

 have brought about profound changes in stream course, diverting and re- 

 diverting flow, lending force to extensive piracies. A dift'erentiated fauna 

 necessarily experienced alterations with these changes. Parts of it were 

 possibly left isolated, to retain characteristics, to intensify them or to lose 

 them — all within itself. Other parts possibly suffered through competition 

 or else interbred with forms of life with which hitherto they had not been 

 in contact. 



M. R. Campbell and C. W. Hayes, in 1894 and 1895, put forth the con- 

 tention that as late as Tertiary times a river comprising the upper Tennessee 

 and the Coosa flowed continuosly southward to the sea, and that — at some 

 period in the Tertiary — a confluent of the Tennessee and one of the Sequat- 

 chie to the west formed a connection through Walden Ridge at Chattanooga 

 and diverted the Tennessee section of the river into an entirely new course. 

 D. W. Johnson reviewed this work ten years later. From studies upon 

 the ground he came to a very decisive opinion that the "Tennessee River 

 acquired its present course across the mountains some time before the close 

 of the Cretaceous period when the present flat top of the mountains was 

 continuous with the rest of the Cretaceous peneplain." To this view C. C. 

 Adams was apparently won. 



The theory of a Coosa-Tennessee River is not necessary to account for 

 the dispersal of the Anculosae. Nor is it needed to explain the existing 

 differentiation. A stream balance prevailing upon the Cretaceous peneplain 

 such as Adams describes would permit of innumerable captures 6i tributar- 

 ies and the transfer and dispersal of their molluscan species. Further there 

 have been opportunities possibly in fairly recent times, geologically speaking, 

 for an interchange of the fauna through stream piracy both to the east 

 and the west of the mountains. Forms of Pleuroceridac in the Hiwassee, 

 highly suggestive of Georgian forms, seem to point to captures by that 

 stream from the Conasauga of the Coosa, the confinement of these forms 

 to the Hiwassee and its vicinity pointing to a time of capture so recent that 

 wide disijcrsal has not yet come about. There is reason, indeed, to believe 

 that not only did the Hiwassee make captures from the Conasauga but that 

 this latter stream also acquired tributaries which originally belonged to the 

 present Tennessee confluent. 



We are to imagine the Cahaba as a small stream in the Cretaceous times, 

 flowing directly to the sea. The I'lack Warrior existed, if at all, either 



