IS THE DAKOTA FORMATION UPPER OR LOWER 

 CRETACEOUS? 



By J. E. Todd, University of Kansas, Lawrence. 



T3ECAUSE of the quite diverse classification of this formation 

 -*-^ by prominent geologists, the writer has desired to find for 

 himself a satisfactory answer to the above question. Thinking that 

 it may be of interest to others also, he offers this paper. 



The formation was first limited and named by Meek and Hayden 

 in 1856. The name was derived from Dakota City, opposite Sioux 

 City, Iowa, and was applied to a thick stratum of rusty sandstone 

 there exposed for 50 or 60 feet, and in other localities found to 

 attain 400 or 500 feet. They recognized its Cretaceous character, 

 but as that system was not very well known, and because the Dakota 

 rests upon the Carboniferous there, it was judged by them to be at 

 or near the base of the Cretaceous. 



In 1859 Beer and Lesquereaux decided that the leaves found 

 abundantly in the formation indicated Tertiary age, but Meek and 

 Hayden showed by the invertebrate life that it was at least Creta- 

 ceous. 



In 1870 Credner pointed out similarities between the New Jersey 

 Cretaceous and the Senonian, or Upper Cretaceous, of Europe, forty 

 species being common to both. 



Dr. C. A. White, in his "Correlation" paper on the Cretaceous 

 (1891 ), concludes that "the Dakota is as clearly distinguishable as 

 a separate formation in the northern and central portions of the 

 south interior region as it is at the typical localities in the northern 

 interior region, in all of which districts the strata are plainly of 

 non-marine origin. In the southern part of the southern interior 

 region, however, as well as in central Kansas and in eastern Texas, 

 the strata which are confidently regarded as representing the Dakota 

 formation are found to bear true marine fossils, and in some cases 

 both paleontologically and stratigraphically to blend so intimately 

 with the next overlying strata, which are regarded as equivalent to 

 the lower part of the Colorado formation, as to render their inter- 

 delimitation indistinct." ^ 



Prof. Lester F. Ward, in 1894, found cycads of the Lower Creta- 

 ceous in the lower part of the Dakota in the southern Black Hills, 



1. U.S. G. S. Bull.. 82, p. 158. 



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