Peneplains of the 0::arlc Highland. — Hcrshey. 2C) 
the same system as those of north Arkansas. One in particu- 
lar near Scholten, in the latter county, is a narrow, flat-topped 
ridge rising about fifty feet above the surrounding plain. 
Coal Measure sandstone and BurHngton limestone are so com- 
bined in its structure as to make its truncated summit difficult 
of explanation under any other than baseleveling conditions. 
I am inclined to believe this is a remnant of the Cretaceous 
peneplain, here only fifty feet above the Tertiary. Northward 
from here, along the so-called "crest" of the Ozarks they may 
be completely merged into one. 
The main Tertiary peneplain. — Between the narrow Oua- 
chita mountain ridges of south-central and southwestern Ar- 
kansas, there are broad basins which, like the inter -montane 
valleys of Pennsylvania, represent the Tertiary peneplain. In 
the vicinity of Mena, in Polk Co., Ark., the surface is gently 
imdulating, the streams not having cut much below the orig- 
inally very flat peneplain. It is here elevated about 1,300 
feet above sea-level, but slopes gently in all directions, partic- 
ularly toward the east and south. Southward from Mena, 
there are tracts of many square miles, where the surface is a 
remarkably level plain. But if we go northward from Mena, 
toward the Arkansas river at Fort Smith, after passing Rich 
mountain through Eaglegap, we find the floors of the inter- 
montane basins quite thorougly dissected by narrow valleys 
separating still narrower ridges. These ridges are long and 
straight, remarkable for their even crests, and for their equal 
bights. In other words, the summit-plane of these ridges 
forms as perfect a dissected peneplain as can anywhere be 
found on the American continent. This imaginary plain is 
absolutely indifferent to the stratigraphy and structure. That 
it represents a base-level of erosion common to the entire 
Ouachita region is demonstrated l)y the fact that its slope in 
each basin is uniform in direction and degree with that of con- 
tiguous basins; that is, were the Ouachita mountains removed, 
and the valleys filled to the level of the long, even-crested 
ridges of the basins, the whole country would be perfectly 
even plain, rising toward a central point near Mena to form- 
a dome-shaped elevation of the land — the Ouachita uplift. 
This is the main Tertiary peneplain of southern Arkansas and 
Indian Territory. Qn it stand the Ouachita peaks and ridges 
