America ol-imit in tiic Cretaceous, a fonnatioii comparatively recent in 

 tlie jjeolou-ical time-scale. Tins formation occupies the greater part of 

 tlie "plains" region west of the Mississippi river and extends from the 

 Gulf of Mexico to the Arctic ocean. It is, in Dakota. Nebraska and Kan- 

 sas, especially rich in vertebrate remains. The same area extends north- 

 east into Iowa, its eastern limit being unknown but being probably some, 

 where between Ft. Dodge and Iowa Falls. The fact that it is covered 

 with Drift to the depth of fifty to one-imndred feet makes investigation 

 almost impossible. 



The only typical exposure of tliis formation is along the Big Sioux river 

 in Plymouth and Woodbury counties. . The exposed portion here is of 

 course very small in comparison with the highly eroded area of Kansas 

 from which Prof Marsh olitained .so many valuable specimens. The 

 Cretaceous in Iowa doubtless extends over nearly one-lialf of the state 

 running far east along the nortlu'ru border and far south along the 

 western. Could the Drift be renuived from tliis area and tlie Cretaceovis 

 studied we would tloubth^ss find as rich deposits of vertebrate remains as 

 in Kansas. 



So far the United States Geological Survey has given no attention to 

 this area and as yet the State survey has done little, the only work here 

 having been done by S. Calvin. State (leologist. 



The results of his work are to found in the proceedings of the Iowa 

 Academy of Sciences for 189:.'. 



Now as to the second cause of non-occurrence i. e. that the Iowa forma- 

 tions are destitute of the remains. While their presence has not been 

 ascertained, their absence on the other hand has not been proved. The 

 evidence going to show that they probably do occur is contained in the 

 following paragraphs. 



Samuel Calvin. State Get)logist. in his study of the Cretaceous deposits 

 near vSioux City has proved beyond a doubt that they represent the Creta- 

 ceous formations of Nebraska and Kansas described by Meek and Hayden. 

 According to Calvin the exposure at Sioux City presents three distinct sub- 

 divisions of the Cretaceous as follows: The lower one consisting mostly 

 of sandstones with a few shales, is the Dakota group. The middle shaley 

 formation represents the P"'t. Uenton group, and the upper chalk deposit 

 is the Niobrara group. 



The last named formation extends over a large area of Kansas and 

 Nebraska and is the formation from which Prof. Marsh has described 

 over twenty species of fossil birds belonging to the orders Odontormae and 

 Odontolcae. That the nature of these fossils may be more plainly under- 

 stood the classilication of birds as given by Marsh is here presented. 



Class Aves. 



Sub Class Ornitlu^s. the iinxlern birds. 

 Sub Class Odontormae. or tootiied birils. embracing 

 Order Saururae. 

 Order Odontolcae. 

 Order Odoutotornuie. 



The first order named, tlie Saururae. is represented by the .Archaeop- 



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