Nonconformities at the Platte River. — Gould. 365 
erous was a marine deposit. The sedimentation was very 
even, the different ledges of limestone and shales often per- 
sist for miles with almost no variation in thickness. (Fig. i.) 
Fig. 1. Carboniferous Sedimentation. 
At the close of the Carboniferous age, or at least during 
the Triassic and Jurassic epochs, the Carboniferous deposits 
were raised above the sea level and denudation began. The 
amount of rock removed during this time must have been 
considerable. In southern Kansas there are some twenty- 
six hundred feet of Permian strata between the Carbonifer- 
ous and the base of the Cretaceous. At the Kansas-Nebras- 
ka line the Permian is not more than two hundred feet thick, 
and it disappears entireh' before reaching the Platte river, 
where the Dakota rests directly on the Carboniferous. 
Whether the Permian strata in eastern Nebraska ever reached 
the thickness attained in southern Kansas is not known. 
However, it is evident that erosion at this time was not 
only considerable but also very uneven. The hills of the 
old Carboniferous rocks were apparently higher and the val- 
leys deeper than those of the same region to-day. (Fig. 2.) 
Fig. 2. Post-Carboniferous Erosion. 
