Peneplains of the Ozark Highland. — Hershey. 37 
era, but the major portion of their excavation seems to have 
been accompHshed during that long, early epoch of the Pleisto- 
cene period marked by an abnormal elevation of perhaps the 
whole of the North American continent, and which has come 
to be known as the Ozarkian epoch or sub-period ; hence, for 
convenience in discussion, I shall refer to the lower troughs of 
the Ozark highland as the Ozarkian valleys. The canyon-like 
form is a characteristic of them which seems to be persistent 
throughout the Mississippi basin, particularly on the lime- 
stone areas. It reaches its most typical development in south- 
central Missouri, along such streams as the Osage and Gas- 
conade rivers and their tributaries. The canyon valleys of 
this region have been so often described that I will merely 
mention the facts that they are steep-sided troughs winding 
about in the bottoms of the basin valleys, have frequently a 
mural precipice on one side and a steep slope, strewn with 
river-gravel, on the other, and are rarely more than several 
times as wide as the streams flowing into' them. The canyon 
valley of the lower Osage averages one-half mile in width and 
about 150 feet in depth. Nowhere else in the Ozark highland 
are the Ozarkian valleys of much greater depth than the Plio- 
cene basin valleys. Throughout the northern slope of the 
Ozark plateau they vary between 100 and 200 feet in depth, 
while the upper troughs are but half as deep. Yet the latter 
are several times as wide, and from their character indicate 
a much longer period of erosion. 
On the so-called "southern slope of the Ozarks" in Mis- 
souri (including the White River basin), the Ozarkian valleys 
are essentially of the same character as that of the Osage, hav- 
ing the meandering courses and the mural percipices. The 
canyon valley of White river in Missouri is scarcely 1,000 feet 
in width and 150 to 200 feet in depth. Winding about in a 
Pliocene basin valley from three to five miles in width and 
nearly 300 feet in depth, the contrast between them is ex- 
tremely marked and significant. Nearly the whole of the 
James River valley and tributaries, such as Flat Creek valley, 
from the main Tertiary peneplain down, has the canyon form 
and winding course, but only the lower sixty to one hundred 
feet is Ozarkian in age, the 200 to 300 feet above the rock- 
terraces being of Pliocene age. In short, in this central por- 
