94 The American Geologist. AuguHt, 1S96 
plain of residua of considerable size but composed of no spe- 
cially resistant strata, and the comparatively small amount of 
subsequent erosion, make it evident that its age is not Creta- 
ceous or earlier ; [b) the amount of erosion accomplished in 
the district subsequent to the uplift of baselevel No. 2, as 
compared with that of other districts in which the age of the 
peneplains and valleys has been determined, makes it equally 
evident that this peneplain is not so young as the Quaternary 
era, and that, consequently, it is a Tertiary peneplain : {<■) 
from its apparent continuity across the central Mississij)pi 
basin to the undoubted Tertiary pene])lain in Tennessee, it 
may be provisionally correlated with the latter. 
The baselevel indicated by peneplain No. 3 of the Freeport 
section, although widely extended through the Driftless Area, 
is probably limited, as an important originator of topographic 
forms, to the vicinity of the "uplifts." This very imperfectly 
developed peneplain may also have been due to a local uplift 
of the upper Mississippi region. It was preliminary to the 
general uplift of the continent which instituted the Quater- 
nary era, and I would class it as late Tertiary. 
The correlation of the canon-like vallej^s is the least ditH- 
cult of all. They belong to a cycle which was characterized 
by the formation of bluffs. This peculiarit}' of the immediate 
valleys of the streams throughout the central Mississippi basin 
is one of the first features to attract the attention of the vis- 
itor. We may leave our district in the valley of the Missis- 
sippi and follow its blulfs (through the preglacial valleys 
around the new gorges at Rock Island and at Keokuk) down 
the river to the embayment region. The surface line of the' 
blulfs makes no abrupt changes in hight, and there can be no 
question of the synchronism of all the valleys of this class in 
Illinois and contiguous states. At the head of the embayment 
region our canon valleys pass under the Lafayette plane. 
Across southern Illinois we can trace the same system of val- 
leys to the Ohio. On the southern side of this stream, in 
Kentucky, they are found to pass under the well established 
Tertiarv peneplain. Hayes and Campbell find the Lafayette 
formation, around the borders of the southern Appalachian 
province, resting on the Tertiary peneplain. If our attempted 
correlation of baselevel No. 2 in northwestern Illinois with tlie 
