IOWA ACADEMY OF SCIENCE 
151 
Swallow’s name, Marias des Cygnes coal-formation, was early and accurately 
defined, and has priority over Pleasanton, and all other names given to the 
uppermost division of the Des Moines series. 
Until quite recently the division of Saverton shales has not been recognized 
in Iowa — the section being commonly merged with the Hannibal shales under 
the title of Kinderhook shales. 
For reasons stated elsewhere the age of the Dodge gypsum is still assigned 
to the Cretacic period. The accompanying reddish or pink shales outcrop in 
Iowa farther north than Fort Dodge. Similar shales are exposed in numeroub 
localities in the adjoining counties of Minnesota. From the latter localities 
Lesquereux has described a number of Dakotan plant remains. The known 
geographical extent of Permian deposition in this country almost completely 
militates against the possibility of these shales being of Paleozoic age, as argued 
by Wilder. The latter’s evidence in support of his contention is very inclusive. 
At the time that Bain named the Riverside sands of Woodbury county and 
showed that they were delimited both above and below by a notable uncon- 
formity they were thought to belong to the glacial deposits. Recent comparisons 
with similar deposits occurring a little further to the west, in Dixon county, 
Nebraska, indicate that these sands are in all likelihood the eastward outlying 
extensions of the Arikaree formation of Miocene age. It is also probable that 
over large areas they underlie the thick drift deposits of northwestern Iowa 
and South Dakota. White, clear-grained, pebbleless sands penetrated in many 
wells seem to belong to this formation rather than to the till-sheets, with which 
they have been usually associated. » 
