The Developnnent of Mississippi. Valley. — Ilershey. 247 
of land, now included in this state, remained above the sea- 
level, except perhaps the extreme northeastern portion of it. 
The isolated outliers which, in Minnesota, indicate the for- 
mer extent of the sea, have all been demonstrated to be upper 
Cretaceous in age. They have lithologie characters peculiar 
to the product of this period, and, moreover, contain a fossil 
fauna and more especially a flora which fix their age beyond 
any doubt. Now, it is obvious that the rock surface upon 
which these strata repose represents approximately the land 
surface of the later portion of the Cretaceous period. I say 
approxiiJiafely, because there may have been slight marine ero- 
sion of the land surface at the time of its submergence. But 
the shallow depressions or valleys in which these strata rest 
show that there was not formed a well-marked submarine shelf. 
Hence, we may consider the surface upon which these strata 
lie, as representing the present attitude of the Cretaceous pene- 
plain. 
By a careful studj^ of these outliers and the altitudes which 
they now attain, we may learn of the amount of deformation 
which this, at present much dissected peneplain, has suffered, 
and also secure data for its location in neighboring states. 
This is the primary object of this paper. 
Peneplains of southeastern 3finnesota* Cretaceous impure 
lignite with associated fossiliferous clays, outcrop in the west 
bank of the Mississippi river, at the mouth of the Two Rivers 
in Morrison county, central Minnesota. They are of fresh 
water formation, but fix the position of the peneplain almost 
as definitely as do those of marine origin. The altitude of tiie 
mouth of the Two Rivers is about 1034 feet above the sea. 
The outcrop of Archean staurolitic schist and diorite at vari- 
ous places along and close to the river but never high above 
it, within the county ten miles northward, seems to indicate 
that this is approximately the altitude of the dissected Cre- 
taceous peneplain in this vicinity. 
In the counties of Hennepin, Ramsey, and Dakota, whieli 
adjoin each other at the junction of the Minnesota and Miss- 
*The information concerning southeastern Minnesota has been de- 
rived largely from the maps accompanying Vols. I and II of the reports 
of the Minnesota geological survey. These maps, although never in- 
tended to represent all the minute details of the topography, are yet 
sufficiently accurate for the purpose to which I have applied them. 
