GypsniJi Deposits. Kcyes 99 
GEOLOGICAL AGE OF CERTAIN GYPSUM 
DEPOSITS. 
By Charles R Keyes, Des Moines, la. 
In his excellent report on the geology of Webster county, 
recently issued by the Iowa Geological Survey, Prof. F. A. 
Wilder ably argues for the Permian age of the Ft. Dodge 
gypsum beds. In this argument several very important phases 
of the problem appear to be entirely overlooked. 
At the time the special report on the gypsum deposits of 
Iowa was published, the history of opinion on their geological 
age was summed up, and reasons given for believing that the 
beds in question were laid down in time subsequent to the Pal- 
eozoic. Since that report was issued, the orogenic history of 
the region has become more clearly understood. The ancient 
physiography of the district has been deciphered in a way 
that proved far more complete than was anticipated. It is to 
some of these phases of the question that attention is now 
called ; but to which j\Ir. Wilder gives no intimation. The 
evidence appears to prove beyond all reasonable doubt that 
the Ft. Dodge gypsum is not of Paleozoic age. 
It is quite manifest that ^^Ir. W'ilder has misunderstood some 
of the chief statements urged, in the special report referred to, 
for the post-Paleozoic age of the Ft. Dodge gypsum. This 
fact has in a measure led to arguments which otherwise might 
not have been made in regard to the Permian age of the gyp- 
sum beds. 
Even casual consideration of the arguments set forth for 
the Permian age of the Iowa gypsum clearly indicates that in 
reality no critical data were obtained. Some of the points 
brought up are among the most forceful in demonstrating 
directly the opposite of what was intended. Attention called 
briefly to these statements will render more comprehensive 
some of the facts discussed. 
The fact that the shales accompanying the Ft. Dodge gyp- 
sum have a pale reddish to pinkish color apDcars to have 
suggested the "Red-beds" of Kansas, so often referred to the 
Permian. It seems that the color association of the formations 
of the two localities was suggested by a perusal of the litera- 
ture rather than actual comparisons in the field. The Kan- 
sas "Red-beds" are entirelv different lithologicallv from the 
