Peneplains of the Ozark Highland. — Hershey. 39 
sheeted with the Lafayette gravels, silt and clay (even "orange 
sand"). Below this level, the Arkansas has excavated a val- 
ley probably three to five miles in width and 100 feet in depth. 
This corresponds to the Ozarkian valleys of south Missouri. 
On the eroded plain country south of the Arkansas river, 
and in the broad inter-montane basins to as far south as the 
Rich mountain, the streams have cut comparatively narrow 
valleys beneath the Lafayette base-level. These may average 
fifty to one hundred feet in depth and are usually of sufficient 
width to afford room for long, narrow farms on their flat bot- 
toms. Their sides are steep, but mural precipices are rare. 
They are canyon valleys in distinction from the basin valleys 
above, but have the can}on form less typically than in south 
Missouri. In Polk count}', which is on the divide between the 
Arkansas and Red river drainage systems and erosion is not 
active, the canydn valleys are hardly represented at all, the 
streams flowing in shallow depressions or "hollows"' on the 
peneplain. Indeed, throughout the Ozark highland south of 
the Arkansas river post-Lafayette erosion has been insignifi- 
cant in results attained, and one almost refuses to believe that 
the shallow post-Tertiary valleys of that region are the equiv- 
alents of the deep valleys of the Ozark plateau anrl the upper 
^lississippi regions. 
The Modern valleys of central Arkansas. — I'nder this 
heading are to be discussed certain small canyons occurring 
along streams tributary to the Arkansas river in central Arkan- 
sas, and which belong to a system, it is beleved. not liereto- 
fore identified and defined in any other portion of the Missis- 
sippi hydrographic basin. That of the Little Cedar creek, 
northeast of Van Buren, was the most typical one observed, 
and a description of it may serve for all. The rock formation 
is a thin-bedded, calcareous shale of the Coal ^Measure series, 
dipping at a low angle but quite perceptibly toward the south. 
In this the creek has excavated quite a large Ozarkian valley, 
with steep sides and a flat rock-floor one-eighth t<3 one-quarter 
mile in width. This rock-floor is very even and is sheeted 
with a few feet of silty alluvium. It bevels tlie edges of the- 
outcropping shales, which dip down stream. 
Xow, the Little Cedar no longer flows over this old val- 
ley floor, but in a tin\' canvon, mostlv twentv to tliirt\- feet in 
