178 GEOLOGY. 



The Cretaceous Period. 



As is well known, the name Cretaceous is taken from the Latin 

 Creta, meaning chalk, which is exceedingly abundant in deposits 

 of this age in Europe. This, the closing period of the Mesozoic 

 or Reptilian Age, is well represented in the rocks of Nebraska. It 

 is somewhat remarkable, however, that no equivalent of the Euro- 

 pean lower Cretaceous has yet been found in the West. The equiv- 

 alent of the lower green sand of the English Cretaceous is there- 

 fore not present here. It is even questionable whether the upper 

 green sand, or middle Cretaceous, is here represented. The follow- 

 ing is probably the explanation of this fact. As has already been 

 stated, the Sierras, Wasatch and Uinta uplifts probably raised with 

 them the adjoining territories that had been covered by the old Ju- 

 rassic seas. During the whole of the period represented by the 

 lower green sand of the European Cretaceous, the entire Rocky 

 Mountain region was dry land. Whether its utmost height was 

 reached at the close of the Jurassic, or whether it continued rising 

 far into the Cretaceous, is only a matter for conjecture. The weight 

 of evidence is, however, at present in favor of the former view. In 

 Europe the lower and middle Cretaceous were periods of subsidence,, 

 and therefore it is probable that this was the case here. This sink- 

 ing extended over a large part of the Rocky Mountain region, and 

 embraced the plains of Nebraska as far east at least as Fort Calhoun,, 

 on the Missouri, and north of that point to a considerable distance 

 beyond it. From Fort Calhoun, the eastern line of subsidence ex- 

 tended in the opposite direction first southward and then southwest- 

 ward, entering Kansas a little west of the Otoe reservation. At 

 least this far east the lower member of our Cretaceous system is 

 found. It may once have covered the whole of the State, as there 

 are indications that it has been removed from the Carboniferous and 

 Permian by denudation. What adds greatly to the probability of 

 this view is the fact that small areas of Cretaceous rocks are marked 

 by Prof. White, in his geological map of Iowa, in the latitude of 

 41 30' as far east as the southeast corner of Guthrie County. If 

 that view is the correct one, then this Cretaceous subsidence extended 

 much farther eastward. 



Divisions of the Cretaceous. — Nowhere in this country is the 

 Cretaceous so well represented as in the far west, and on the upper 

 Missouri. The following is the detailed section prepared by Meek 

 and Hayden. Having gone over much of this ground myself,. 



