'2ij2 The American Geologist. October, 18'j7 
the topographical development of southeastern Minnesota, 
we will begin in the southeastern corner of the state. Here, 
as we have just seen, the Cretaceous peneplain is represented 
by upland areas which now attain an altitude of 1300 or more 
feet above the sea. This plain must have originally extend- 
ed to and across the present course of the Mississippi, rising 
slightly in that direction; but it has been almost completely 
destroj^ed throughout the country east of the Trenton escarp- 
ment, by erosion subsequent to the uplift of the upper pene- 
plain. This new cycle of erosion resulted in the formation of 
a new peneplain about 150 feet lower than that of Cretaceous 
age. This new peneplain, (whose existence as such is not doubt- 
ed by niost students of the upper Mississippi region) being of 
later age than the Cretaceous may be designated as the Terti- 
ary peneplain. The newer baseleveled plain which has an al- 
titude of about 1200 feet in the southeastern corner of the 
state, slopes gently and evenly northwestward to about 1050 
feet above the sea in Goodhue county. Returning now again 
to the Cretaceous peneplain we find that it slopes northwest- 
ward also gently and evenly, but at a rate slightly greater 
than the Tertiary peneplain, the result being that in Good- 
hue county, where its position is accurately fixed by an exten- 
sive outlier of Cretaceous strata, it is but little higher than 
the Tertiary peneplain. Still farther northward in the vicini- 
ty of St. Paul, the two peneplains have merged so completely 
that either name may be applied to the 900-foot plain with 
equal propriety. Northward from Hennepin count}^ the Cre- 
taceous peneplain again rises, but the country being heavily 
drift covered the Tertiary peneplain is unrecognizable, if, in- 
deed, it is not identical with the Cretaceous. 
Sometime after the termination of the Cretaceous submerg- 
ence of southeastern Minnesota- the land was elevated b}'^ a 
differential uplift. In the extreme southeastern corner of the 
state the elevation was sufficient to enable the streams to low- 
er their channels to about 150 feet beneath the Cretaceous 
peneplain. But in the Minnesota depression wllich extends 
east and west across the south central portion of the state the 
uplift was not sufficient to seriously affect the streapi level. 
Hence, we may infer that about St. Paul and westward in tlie 
line of the structural depression just mentioned, the lanJ sur- 
