I02 The American Geologist. August, 1902. 
believing that any part of this great section was removed 
through erosion during the Paleozoic times. 
In the distance of 200 miles, as the crow flies, between the 
nearest Kansas and Iowa gypsum beds there is a bevelling of 
strata which begins some distance west of the first named 
locality and at a stratigraphic level considerably higher, and 
extends northeastwardly beyond Ft. Dodge and stratigraphic- 
ally below the rcjcks in which the gypsum of the last men- 
tioned place lies. This bevel-plane represents Cretaceous pene- 
planation. The Kansas gypsum Hes below and entirely with- 
out. The Iowa gyjisum lies immediately above the level where 
this Cretaceous plane should emerge at the present surface of 
the ground. Fort Dodge is on the eastern boundary of the 
Cretaceous in Iowa. It is also exactly at the point where the 
Cretaceous peneplain, bevelling the Paleozoics at a given angle, 
is cut by the Tertiary peneplain, bevelling both Paleozoics and 
Mesozoics at a very different angle. 
If the so-called Permian deposits ever existed over the 
present site of Ft. Dodge they were long since removed by 
Cretaceous erosion, and more than 2000 feet of other Carbon- 
iferous sediments besides. Even if the Permian of the region 
had escaped Cretaceous erosion, there was still Tertiary eros- 
ion to remove it, and the Coal IMeasures, down to the same 
level. 
The assignment of a Permian age to the Ft. Dodge gypsum 
deposits appears to be entirely precluded by all direct evidence 
available. The only question regarding the geological age of 
these beds seems to be whether they are Cretaceous or Ter- 
tiary; not whether they are Cretaceous or Carboniferous. On 
the first mcntionel point there have been as yet no direct 
data obtained. In the special report upon the Iowa gypsum 
deposits, published seven years ago, I endeavored to present 
the facts which were thought to be conclusive proof of the 
post-Paleozoic age of the beds. In urging this opinion I ])er- 
haps unconsciously emphasized too strongly and too specific- 
ally the Cretaceous aspects of the problem. 
A Cretaceous age for the Ft. Dodge gypsum deposits ap- 
pears the most probable at present writing, especially when 
the problem is viewed in the light of physiographic criteria. 
A Tertiary age for these beds is not beyond a possibility. A 
Permian age seems entirely impossilile. 
