360 Branner — Former Extension of the Appalachians 



was probably the barrier made by the Ouachita anticline and 

 its eastward and westward extension. 



Reversed Carboniferous drainage in Texas. — In Texas there 

 has been a similar reversal of the drainage over the Car- 

 boniferous area. Even now, and in spite of an eastward tilt- 

 ing of the region, the Carboniferous rocks of Central Texas 

 dip gently westward while the Colorado, Brazos and Red 

 rivers flow southeast or eastward against the dip. Dr. N. F. 

 Drake, who studied the area, believes, from internal evidence, 

 that the sediment came from the east* They are said by 

 Professor Hill to have been covered by Cretaceous rocks :f in 

 this case the present southeast drainage across the Carbonifer- 

 ous has been superimposed, but in any event it has been 

 reversed. Additional evidence of the southeastward origin of 

 the Carboniferous sediments of central Texas is given under 

 the head of " Carboniferous sediments." 



The submerged end of the Ouachita uplift. — A geologic 

 map of the State of Arkansas shows the Ouachita anticline to 

 have an east-west axis and a core of Lower Silurian rocks 

 (though some of them may be older). The western end of 

 this anticline tapers to a point in the western part of the state, 

 and the Lower Coal Measures rocks swing round and dip away 

 from it on all sides. It is reasonable to suppose that its eastern 

 end had a more or less similar form, but it is now concealed by 

 Cretaceous and Tertiary rocks that lap over and across it in 

 such a manner as to give it the appearance of having been cut 

 almost square across — an appearance that could have been pro- 

 duced only by the lowering of this eastern end beneath the 

 Cretaceous and Tertiary seas, and the deposition of their sedi- 

 ments upon it. (See accompanying plate showing the Oua- 

 chita anticline.) 



Slope of the Ouachita uplift. — The slope of the Ouachita 

 uplift is toward the east. This is true both of the general 

 surface and of the higher elevations over the entire area. The 

 general level of the highest of the Silurian peaks about the 

 eastern end of the Ouachita anticline is between 500 and 600 

 feet above sea level, while the general elevation of the same 

 novaculite rocks about Hot Springs is about 1200 feet, and 

 south of Dallas, Arkansas, at the western end of the anticline, 

 about 1900 feet. The greatest elevations in the western part 

 of the state, however, are in Lower Coal Measures rocks : the 

 highest of these are between 2750 and 2825 feet ; Shinall 

 Mountain, the highest mountain of Carboniferous rocks at the 

 eastern end of the Carboniferous area, is 1050 feet high, while 

 most of the high points about this eastern end are between 



* Fourth Ann. Eep. Geol. Survey of Texas, 1892, p. 373. 

 f Bull. Geol. Soc. Amer., ii, 527. 



