PHYSIOGRAPHY OF THE BOSTON MOUNTAINS 699 



recent writer' claims that the tops of the Boston Mountains 

 represent a peneplain, and cites as evidence the fact that they 

 correspond very closely in height with the Ouachita Mountains 

 south of the Arkansas valley. This evidence is given on the 

 assumption that the rather uniform height of these mountains 

 represents a peneplain ; but this is a hypothesis far from being 

 established. Mr. L. S. Griswold, in his work on the novaculite 

 region of Arkansas, encountered the problem of the noncon- 

 formance of some of the main streams of the region to the 

 structure and topography, to account for which he presents the 

 theory of a post-Carboniferous base-level, on which was subse- 

 quently deposited Cretaceous strata.^ If the present writer 

 correctly interprets Mr. Griswold, he believes the south-flowing 

 streams, which form water-gaps in some of the highest moun- 

 tains of the region, are superimposed streams, their courses 

 having been determined by the slope of the Cretaceous area 

 after elevation. Mr. Griswold does not claim that the evidence 

 of this is conclusive. It is the opinion of the present writer, 

 from somewhat limited observation, that the even crests of the 

 Ouachita Mountains are due to structural and lithological con- 

 ditions and not to base-leveling. But were it established that 

 they represent a peneplain, the fact that the Boston Mountains 

 closely agree with them in height does not argue a peneplain 

 for the latter. The one is a folded area, and the other an area 

 of horizontal rocks (Fig. 2). Erosion in the one has resulted 

 in wide, anticlinal valleys through which flow sluggish streams, 

 while erosion in the other is in its early stages. It would seem 

 to follow that the time of elevation of the one region is far ante- 

 cedent to that of the other, and consequently the correspon- 

 dence in height between the two only accidental. 



If, however, we look to the north of the Boston Mountains, 

 we find conditions which seem to throw some light upon the 

 subject. As has already been said, this is a region of great 

 denudation. Its general elevation is from 700 to looo feet 



'O. H. Hershey, ^w. Geologist, Vol. XXVII, No. i, pp. 25 et seq. 

 ^ Ark. Geol. Siirv., 1890, Vol. Ill, pp. 220. 



