CRETACEOUS SYSTEM. 289 



of Meek and Hay den, nor any doubt that the lowest portions 

 of onrs is equivalent to a part of their Dakota group. 



All the Cretaceous strata of Iowa are of course a part of 

 the same deposits as those farther up the Missouri river, and 

 in reality, constitute their most easterly extension. Although 

 they are in our State of little thickness compared with 

 those, they are yet properly separable into three distinct 

 subdivisions ; and with no intention of superceding the 

 names in their general application which those gentlemen have 

 proposed for the more general subdivision of the strata 

 where they are more fully developed, the following names are 

 used in this report to designate the subdivisions of the 

 Cretaceous strata as found in Iowa. 



They are named in their natural order, the most recent 

 formation first: 



Inoceranius beds 50 feet. 



Woodbury sandstones and shales 150 feet. 



Nisnuabotany sandstone 100 feet. 



The maximum thickness of each is given so far as known 

 in Iowa. 



Besides the following general descriptions of each of these 

 three formations, more detailed descriptions will be found in 

 the chapters upon the Middle Region of Western Iowa and 

 Southwestern Iowa, where also sketches and diagrams are 

 introduced for illustration. 



2. THE NISHNABOTANY SANDSTONE. 



This formation is found well exposed at several points in 

 the valley of the East Xishnabotany river, from which 

 circumstance it has received its name. It has the most 

 easterly as well as the most southerly extent of any of the 

 Cretacous deposits of Iowa, being found as far east as the 

 southeastern part of Guthrie county, and as far south as 

 the southern part of Montgomery county. To the north- 

 westward it passes beneath the Woodbury sandstones and 



shales , the latter in turn passing beneath the Inoceranius or 

 37 



