26 , The American Geologist. January. 1901. 
structural and physiographic as well as a topographic depres- 
sion. 
South of the Arkansas valley, the country is characterized 
by the long, narrow east-west ranges of the Ouachita moun- 
tains, surmounting a dome-shaped "uplift" or elevated area of 
the deformed Tertiary peneplain. These ridges are truly 
mountains, and bear a marked resemblance, both in strati- 
graphy and structure, to portions of the Appalachian moun- 
tain system. They correspond to the Blue mountains and 
similar ridges in Pennslyvania, east of the main Alleghany 
range. 
The synclinal trough of the Arkansas valley has no rep- 
resentative in the Appalachian region, but topographically the 
valley of east Tennessee is its counterpart. The former sep- 
arates the true mountain portion of the Ozark highland from 
the northern or plateau division. This latter is what is com- 
monly known as the "Ozark uplift," and many would restrict 
the name Ozark to it. The plateau is a great dome-shaped, 
elevated tract of the deformed Tertiary peneplain which at- 
tains a maximum altitude of about 1,750 feet A. T. in north- 
western Arkansas near Fayetteville, and slopes thence gently 
to the north and east, and more steeply toward the west and 
south. It is surmounted, along a line 20 to 30 miles north of 
the Arkansas river, by an east-west range of mountains com- 
monly referred to collectively as the Boston mountain. This 
corresponds to the Cumberland and main Alleghany ridges of 
the Appalachians, and the broad plateau north of it is the 
counterpart of the Alleghany plateau. 
This close resemblance of the physicial features of the 
Ozark highland and the Appalachian mountain region has 
frequently been commented on. It is also known that the his- 
tory of the physiographic development of the two areas has 
been essentially alike in character, as all orographic and epei- 
rogenic disturbances of the one have affected the other also. 
However, the geomorphology of the Ozark province is not so 
well known as that of the Appalachians, and a generalization 
of its physiographic features may be of interest, if not also 
instructive, to students of American geology. 
The Cretaceous peneplain. — This, as Mr. L. S. Griswold 
has identified it, emerges from beneath the Cretaceous strata 
