368 Branner — Former Extension of the Appalachians 



characteristic of Appalachian geology. But if the Ouachita 

 uplift is the structural equivalent of the Cincinnati-Nashville 

 anticline, then it was a region of shallow water at least, and 

 during the land periods turned the drainage from the Indiana- 

 Illinois basin westward through the Arkansas valley. This 

 major anticlinal axis extended westward through the Arbuckle 

 mountains of Indian Territory and ended with the Wichita 

 mountains in southern Oklahoma Territory. The Appalachian 

 system crossed the present Mississippi valley further south, 

 and there was another broad syncline between that watershed 

 and the Ouachita region, and the drainage flowed westward 

 through this valley across south Arkansas, Louisiana and 

 northern Texas, and entered the Carboniferous sea south of the 

 Arkansas valley discharge. 



That this last is the correct theory is borne out by the facts 

 that follow : 



Southern origin of the Ouachita sediments. — The Paleozoic 

 sediments on the south side of the Ouachita uplift are coarser 

 than the materials of the same beds on the north side. This 

 peculiarity is noticeable even in the Silurian novaculites : those 

 on the south "are pure in composition and massive, while on 

 the north side they have largely the character of siliceous 

 shales."* Again, the beds overlying the novaculites on the 

 south are sandstones, while on the north they are shales. These 

 facts seem to place the Ouachita uplift, in its relations to the 

 source of its sediments, in a position analogous to that of the 

 Cincinnati and Nashville arch whose sediments are supposed 

 to have been derived from the Appalachian lands. 



The Carboniferous sediments. — The accompanying map 

 shows the varying thickness of the Carboniferous rocks. It is 

 noticeable that the greatest thickness is in the Arkansas-Indian 

 Territory valley, in central Texas, in western Pennsylvania, 

 and in northwestern Alabama. Attention should be directed 

 to the fact that only the upper part of the Texas Carboniferous 

 beds is uncovered. On the Brazos River, southwest of Weath- 

 erford, Fusilina limestone is exposed, showing these beds to 

 belong to the Upper Coal Measures. But these rocks are not 

 the highest, but the lowest, exposed in the central part of the 

 Texas Carboniferous area.f The Texas coal is therefore 

 higher up than is the coal of Indian Territory and Arkansas. 

 This shows that coal-forming conditions prevailed in Texas 

 later than in Indian Territory and Arkansas. It cannot be 

 said that the Arkansas basin shallowed earlier than that of 

 Texas, for the Texas beds of equal age with the lowest coal of 

 Arkansas are concealed by Cretaceous rocks. 



*L. S. Griswold, Geol. Sur. Ark. Ann. Eep., 1890. iii, 193. 

 f Communicated by N. F. Drake. 



