362 Branner — Former Extension of the Appalachians 



500 and 750 feet above sea level. If we take the lowlands we 

 have an elevation of 500 feet about Fort Smith, and of 250 to 

 300 feet about Little Rock. The fall of the Arkansas river 

 from Fort Smith to Little Rock, a distance of 140 miles on a 

 line, is about 200 feet. A reversal of the drainage of the main 

 stream from Little Rock to Fort Smith only with the same 

 slope, would require an elevation of 400 feet at Little Rock. 

 Or the reversal of the drainage from the Mississippi river to 

 the Permian border, 100 miles west of Fort Smith, would 

 require an elevation of 925 feet at the Mississippi river. And 

 it is interesting to note that if the Mississippi region about 

 Memphis and Helena were brought up to a level with the base 

 of the Permian in Indian Territory it would be about on a 

 level with the Carboniferous of southern Illinois, Indiana, 

 western Kentucky, Tennessee and Alabama. This does not 

 take into account the removal of Carboniferous rocks by 

 erosion. 



Drainage of the Ouachita uplift. — An examination of the 

 accompanying map shows that the drainage of the Ouachita 

 mountain region is now only partially controlled by the 

 structure, and, as the tendency is for the structure to con- 

 trol it more and more, it is fair to assume that not long ago it 

 was less influenced by the structure than it is at present. The 

 present elevation of some of the Tertiary beds near the Silurian 

 area lead me to believe that during Tertiary times nearly all 

 the lower portion of the Ouachita uplift region was covered by 

 water and sediments. This would account for the drainage, 

 but inasmuch as there is a general southeastern direction to the 

 streams (the Ouachita, the Saline, and the Caddo), the slope of 

 the Tertiary surface as it emerged must have been toward the 

 southeast — in the direction of the principal axis of disturbance. 

 This will be the more apparent if it be remembered that the 

 Silurian rocks across which the several forks of the Saline, the 

 Ouachita and the Caddo flow, are largely novaculites — ex- 

 tremely hard and resisting rocks which stand out in high, 

 almost perpendicular ridges. 



Faults in Arkansas and Indian Territory. — The faults and 

 folds across the eastern end of the Boston Mountains and close 

 to the depressed area are approximately parallel to the Cre- 

 taceous and Tertiary margin. This margin has a direction of 

 North 30° to 35° East. The folds through the Arkansas val- 

 ley are approximately east-west, but about the eastern end of 

 the Boston mountains they swing away toward the north, where 

 they bear North 50° East.* 



It was hoped that the faults in the State of Arkansas might 

 throw much light upon the subsidence under consideration. 



*Newsom and Branner, Amer. Geol., July, 1897, xx, pp. 1-13. 



