MEDIiEVAL OR MESOZOIC TIMES. 197 



CHAPTER III. 



MEDLEVAL OR MESOZOIC TIMES IN NEBRASKA, 



CONTINUED. 



Fort Pierre Group Cretaceous. — Its Position and Extent. — Thickness. — 

 Life of this Epoch. — The Fox Hills Group. — Its Exposures, Character and 

 Extent. — Its Vegetable and Animal Life. — Laramie Group. — Where Exposed, 

 and Probable Presence in Nebraska. — Conformability to the Preceding 

 Groups. — Whence its Materials were Derived. — Its General ( haracter and 

 Thickness. — By Whom Explored. — Its Great Extent. — Its Characteristic 

 Feature. — Character of its Flora, and the Great Number and Modern Char- 

 acter of its Species. — Animal Life, made up of Marine, Brackish and Fresh 

 Water Species. — Reptilian Remains. — Transition Character of this Group. — 

 Probable Existence of Coal in the Cretaceous Groups in Nebraska.— How 

 this can be Ascertained. — Close of the Cretaceous and Transition Period. 



Fort Pierre Group 



THE preceding (Niobrara Group) era came to a close by a con- 

 tinuation of that process of elevation that eventually drained 

 the region where its deposits now constitute the surface rocks. 

 Here and there the deeper portions of the old sea beds were still 

 filled with water It is doubtful, however, whether these Fort 

 Pierre seas in Nebraska were at this time connected with the Ocean. 

 However that may.be, the filling up of these seas gave us the pe- 

 culiar deposits of this era. It is possible that the elevation going 

 on at the close of the preceding era continued until the whole State 

 was a land surface. The great inequalities of the Niobrara group, 

 on which this group was laid down, suggests this explanation. It 

 is hard to conceive a sea bottom so uneven and irregular. If, how- 

 ever, it was first elevated into dry land, and exposed to sub-aerial 

 action, which produces inequalities of surface, its broken character 

 is accounted for. 



Two regions of Nebraska contain these deposits. One of them 

 is in northeastern Nebraska, in Knox County, below the mouth of 

 and for a short distance along the Niobrara. The other is on the 

 Upper Republican, towards the west line of the State. 



The m iterials of the Fort Pierre group, in Nebraska, are made 

 up largely on the Upper Republican, of occasionally thin beds of 



