24 The American Geologist. juiy. 1901. 
greater width than that at Ahjl)crl}' in northern Missouri. It is 
iounded on either hand l)y more deeply trenched valleys than 
tiiose in the neighhorhood of the Moberly i:)lain. 
In general, 1 should say that under like conditions as to 
stream gradient, the valleys of southern Missouri are about 
twice as large as those of northern !^Iissouri. Of course, the 
Ozark region has been abnormally uplifted and in a large por- 
tion of it erosion trenches are much deeper than in any part of 
northern Missouri, but where conditions have been essentially 
alike (except for material eroded) there is far from as great 
difference in excavation accomnlished as we should expect ex- 
cept under our previous conceptions of the age of the Kansan 
drift sheet. 
If we compare the valleys of northern Missouri with that 
portion only of the valleys south of the Missouri river which is 
below the supposed Lafayette base level,* it will appear that 
there is scarcely any difference in the amount of material re- 
moved by streams of an ec|ual size and an equal gradient ; if 
there is any difference it is in favor of the post-Kansan valleys 
of the drift area. However, we must remember that the valleys 
(-f one region are carved almost exclusively in drift and in the 
G^her in solid rock. There are many places in the glaciated 
area where the difference in power of resistance to erosion of 
ordinary till and such rock as commonly occurs in the Mis- 
sissippi basin may be observed. The ratio is not less than as 
I 15. It is therefore certain that the valleys of northern Mis- 
souri have not been exposed to erosion as long as the post- 
Lafayette valleys of southern Missouri, and we have no reason 
for carrying the age of the Kansan drift back into the Tertiary 
era. Indeed, from the relation along the boundary of the 
glaciated area of the drift sheet and valleys in solid rock, it ap- 
pears that the latter had been eroded to largelv their present 
extent before the Kansan epoch. There are not yet known 
any clear cases where this may be studied, but it is known that 
the rock surface under the drift of northern Missouri is very 
uneven and contains valleys such as the Ozarkian vallevs of 
southern Missouri. 
I have detected what I consider evidences in the Kansan 
area near Higginsville, about 30 miles north of the Missouri 
'"Peneplains of the Ozark Highland," Am. Geo!., Jan., 1901. 
