90 I'lie American Geoloyisl. August, lisoo 
distance of fifteen to twenty miles from the border, tlie ])lain 
as such is no longer seen, but we have the projected position 
of the plain surface indicated by the uniformity in the eleva- 
tion of the crest lines of the ridges/' Unless some remark- 
able axis of deformation occupies the position of the Arkansas 
valley, this same peneplain is re])resented by tlie Boston 
mountains at an elevation of 2,000 feet above the sea. Thence 
it gradually slopes to the north, and in south central Missouri 
passes across the higher upland surface atan altitude varying 
between 1,350 and 1,500 feet. The Ozark plateau bears the 
same relation to the mountain system of central Arkansas as 
the Cumberland and Alleghany plateaus do to the Appalach- 
ians. From the valley of White river in southern Missouri to 
the so-called " crest" of the Ozarks, the general upland sur- 
face is nearly level, but descends very slightly to the north 
against the prevailing direction of drainage. 
Beyond the "crest" the ui)land slopes rather rapidly toward 
the Missouri river; and there the Cretaceous peneplain has 
probably been largely destroyed. This is apparently true also 
on the eastern slope of the Ozark uplift. But from the axis 
of deff)rmation of the Cretaceous peneplain to the Missouri, 
the two baselevel planes — elsewhere designated as ('retaceous 
and Tertiary — have been gradually converging and probably 
merge into each otlier along some line in northern Missouri. 
The upper peneplain being entirely destroyed throughout a 
large area surrounding the district in which they merge, the 
truth of this proi)osition can only be determined by the dis- 
covery of Cretaceous strata within this district near the same 
level at which the Tertiary peneplain appears. For the above 
reason, also, it is very ditHcult to locate the Cretaceous pene- 
plain in northwestern Illinois b}^ direct tracing alone. We 
ma}^ follow one peneplain down to the level of a later one, on 
one side of the "merging" area ; but we cannot say, with full 
confidence, that the penejjlain which rises on the other side is 
strictly contemporaneous with it. 
Hayes and Campbell* have definitely located the Cretaceous 
peneplain in the southern Appalachians, and, tracing it west- 
ward across the ('umberland plateau, they find it represented 
*Geomorphology of the Southern Appalachians, National Geographic 
Magazine, vol. vi, pp.-G3-12G. 
