252 University of Kansas Geological Survey. 
ment was correspondingly rapid and the filling in process carried to 
a great extent. 
Kastward from the mountains the material was likewise carried 
in vast quantities and spread out over the present plains area. It 
was not accumulated to such great depths, the thickness rarely ex- 
ceeding 1000 feet, while over the western part of Kansas we no- 
where find it at the present time more than 350 feet thick. The 
mountainous elevation was probably less during early Tertiary 
times than at present. The drainage which carried the debris east- 
ward seems to have been fluctuating in character, at times flowing 
with a strong current, as is shown by the coarseness of the material 
carried, and at other times moving with a mild current, so that only 
the finer sediments could be carried and deposited. 
The floor upon which the Tertiary material was deposited was 
principally a Cretaceous floor, one which doubtless had been elevated 
above the ocean water for a sufficient time over the greater part 
of the area to have its surface greatly corroded by the weathering 
agents until it presented an irregular surface. If the corrasion 
of the Cretaceous surface occurred after the entire inland ocean was 
destroyed the drainage producing such a corrasion must have been 
eastward. It is difficult to understand why such a drainage would 
not carry debris from the mountainous areas the same as a similar 
drainage did at a somewhat later period. It seems probable there- 
fore that the eastward movement of the debris began about the 
time the corrasion of the Cretaceous surface began, and that the 
two processes were carried on to a great extent simultaneously. 
Possibly the particular character of the surface drainage was such 
that relatively large areas on the plains received no material from 
the mountains for a time, corresponding somewhat to the present 
condition with so many streams rising farther east than the limits 
of the mountains. In this way sediments may have been forming 
over certain parts of the plains during the earlier Tertiary or Eocene 
period, a corrasion of the surface of other portions taking place at 
the same time. By slight change of elevation in the plains, or in the 
mountains, at a somewhat later date the conditions could have 
been changed so that the areas before disconnected from the moun- 
