32 The American Geologist. January. 1901. 
the surface. Here the plain-Hke character of the country in 
the Tertiary era has not been destroyed. The land is gener- 
ally rolling, and the '"crest" gently ascends and descends, but 
it is evident that it is the same plain which is being followed 
from end to end. 
This Tertiary peneplain descends very slowly from its 
maximum of about 1,700 feet in northwestern Arkansas, to 
about 1,500 feet on the Pea ridge, where it is crossed by the 
Missouri line, and thence to 1,300 feet near Springfield and 
Lebanon. A local uplift of no great extent seems to elevate 
it to about 1.700 feet at Cedar gap in Missouri. The White 
River valley in Missouri occupies a kind of depression in the 
surface of the peneplain. The same Tertiary base-level is 
represented by the main ridges of the undulating plain about 
Joplin in extreme southwest Missouri, at about 1,000 feet A. 
T. It is the same peneplain which forms the general upland 
surface of eastern Kansas. Thence southward through In- 
dian Territory it may be traced around the Boston mountain 
to the Tertiary peneplain in the Arkansas valley, thus escaping 
the complication of the curious monocline on the southern 
slope of the Boston range. 
North of the so-called "crest" of the Ozarks in southern 
Missouri, the peneplain continues to descend gradually, and 
has no greater elevation than about 900 feet at Boonville and 
Jefferson City on the Missouri river. The highest hills in 
the vicinity of both towns represent it. It is much dissected 
all along the Missouri river, but there are enough remnants 
left to demonstrate that it is present on both sides of the com- 
paratively narrow valley. 
The Lafayette base-level. — In that portion of the Ozark 
highland which is south of the Arkansas river, a large part of 
the surface has been reduced by erosion below the main Ter- 
tiary peneplain to a later and relatively low'er base-level. This 
Pliocene or late Tertiary cycle of erosion resulted in the for- 
mation of broad, shallow basin valleys whose floors were once 
quite flat, being composed of the broad alluvial plains of the 
streams of that period. They are now dissected by the canyon 
valleys of later age, and may easily escape detection except 
upon close observation. In approaching the Arkansas river, 
these basin valleys become quite pronounced, spreading out 
