PARTLY DISSECTED PLAINS IN JO DAVIESS COUNTY 423 
within these two quadrangles are not sufficient to determine 
whether the upper plain—that is, the one lying above the Niagara 
escarpment—is a peneplain or a structural plain, and its general 
history outside of these two quadrangles has not yet been com- 
pletely worked out, though its age is probably Cretaceous.” <A 
plain probably to be correlated with the Niagaran plain was recog- 
nized and called the ‘‘Allamakee Peneplain” by Calvin" in his 
report on Allamakee County, Iowa. The intermediate plain has 
been referred to by Hershey as ‘‘Peneplain No. 2,” and by Bain, 
and by Grant and Burchard as the ‘Lancaster Peneplain,” and it 
has been assigned by them to the Tertiary period. Calvin and 
Leonard make no note of such a plain in the reports on Allamakee 
and Clayton counties in Iowa. The Cretaceous and Tertiary ages 
of these respective plains seem to have been tentatively established 
by their relation to Cretaceous deposits in Minnesota and Iowa, 
and to Tertiary deposits in the Gulf region. There is little or no 
evidence of the dates of formation of the plains in Jo Daviess 
County, and their ages do not form the problems of this paper. 
It seems advisable here to describe and interpret these plains, 
as seen in Jo Daviess County, with a view to determining if there 
are any other possible explanations beside that of peneplains. 
The purpose of the discussion is twofold. First, it is hoped that it 
may lead to a true interpretation of these plains and an understand- 
ing of the physiographic history of the region in which they are 
found. Secondly, an attempt is made to bring out the criteria 
for distinguishing upland plains of certain origins and histories 
from those of other origins and histories. It is believed that 
criteria for distinguishing raised and partly eroded peneplains in 
regions of folded strata, such as the Appalachian Mountains, are 
fairly well worked out; but that many of these criteria will not 
apply in regions of horizontal or nearly horizontal structures, and 
that the characters of peneplains in such regions are not so well 
known as they should be and have not been given as critical study 
as they deserve. 
THE NIAGARA PLAIN 
In most places where the Niagara dolomite is found in Jo Daviess 
County, its top has an even skyline when seen from a distance and 
a flat surface as seen when it is traversed. It is always a hard 
* Geology of Allamakee County, p. 43. 
