56 STANTON: UPPER CRETACEOUS STRATIGRAPHY 



the examples entirely from the region of the Rocky Mountains 

 and adjacent plains, from central New Mexico northward to the 

 Canadian boundary and confining them to that part of the Upper 

 Cretaceous column which is within the limits of marine sedimen- 

 tation for the region and does not involve any possible uncon- 

 formities. 



The classic upper Missouri section of Meek and Hayden- 

 recognized only five formations, viz. : 



feet 



Fox Hills sandstone 500 



Fort Pierre shale 700 



Niobrara limestone 200 



Fort Benton shale 800 



Dakota sandstone ■ • 400 



(See Section No. 1, p. 58) 



The thicknesses given were of (bourse mere estimates based 

 on rapid reconnaissance over great distances, the type localities 

 being scattered from eastern Nebraska to central Montana. 

 The section actually passed far to the west of the area in which 

 the Niobrara limestone is developed and crossed a region where 

 a large part of the Pierre shale is represented by littoral, estuarine, 

 and terrestrial deposits. With his standard Cretaceous section 

 recognizing only two sandstones, one at the top and the other at 

 the bottom, it is no wonder that Hayden wavered in his assign- 

 ment of the sandstones beneath the Judith River formation, 

 sometimes referring them doubtfully to the Dakota and later 

 correlating them with the Fox Hills. 



The geologists of the Fortieth Parallel Survey found that the 

 Niobrara did not retain its lithologic character so as to be recog- 

 nizable over a large part of the area surveyed by them and they 

 therefore attempted to map as one great shale group all the rocks 

 lying between the Dakota and the Fox Hills. They also apprec- 

 iated the fact that the Cretaceous sediments in the neighbor- 

 hood of the Wasatch Mountains, at Coalville, Utah, for example, 

 include an unusual development of sandstones thruout the 

 section, which they attributed to near shore conditions, but if 

 they did not succeed in making a consistent map and section of 

 the Upper Cretaceous it was largely because they adopted the 



2 Proc. Acad. Nat. Sci., Philadelphia, 1861, p. 419. 



