TERTIARY HISTORY OF THE TENNESSEE RIVER 



195 



is cut in the high, flat- topped mountain known as Walden Ridge; 

 and then bends southward again in a longitudinal valley similar to 

 the one it occupied before entering the gorge. Both of the longi- 

 tudinal valleys are opened on anticlines of easily eroded limestone, 

 while the transverse gorge cuts across a shallow syncline of resistant 

 sandstone underlain by limestone. The turn of the river from the 



Fig. 1. — Location map. 



broad longitudinal valley abruptly westward through a high moun- 

 tain barrier presents a problem that has interested physiographers 

 for some time. 



Two hypotheses have been advanced in explanation of this prob- 

 lem. According to one, the river acquired this course across the 

 mountain some time before the close of the Cretaceous period of 

 baseleveling, probably near the close of that period, when the present 

 flat top of the mountain was continuous with the rest of the Creta- 

 ceous peneplain ; after later uplift the river continued to flow in that 

 course throughout the Tertiary and Recent cycles, cutting its narrow 

 transverse gorge below the level of the Cretaceous peneplain at the 



