Haworth. | Physiography of Western Kansas. 15 
Yertiary material began to admit of erosion of the Cretaceous sur- 
face almost as extensively as that which is now observed on the 
surface of the Tertiary. Streams of different sizes existed in many 
places cutting their channels sometimes wide and deep, elsewhere 
to a milder degree, leaving a corrugated Cretaceous surface to be 
covered later by Tertiary materials. 
If we accept the view, which seems to be established for the 
Dakotas, of the former existence of a northern Tertiary lake, the 
Sioux lake of King!, it might seem reasonable to suppose that like- 
wise the greater part of the Tertiary materials in Kansas were 
accumulated at the bottom of fresh water lakes. It is almost cer- 
tain, however, that at least a considerable part of this material was 
deposited in place by rivers rather than in the bottom of lakes, and 
that therefore the different drainage channels which have existed 
since the beginning of Tertiary time in Kansas have migrated back 
and forth across the great plains, depositing different kinds of 
material in the irregular form in which we now find them. 
It would be interesting to study the life history of these different 
streams, and to determine whether or not they were originally at 
all similar to the various streams crossing Kansas from the west 
at the present time. With the evidence already alluded to regard- 
ing the probable condition of drainage in the earlier Tertiary there 
is no special reason for not believing that the migration of the dif- 
ferent streams has been sufficient in the aggregate to accomplish 
the main part of the results as we now see them. Should this be the 
case it is probable some of the erosion in the Cretaceous has taken 
place very recently. In fact, different ones of the lesser tributaries 
at the present time are cutting their channels into the Cretaceous 
throughout a part of their course and having their valleys filled in 
with Tertiary material from the adjacent bluffs in other places. It 
seems quite possible that some, at least, of the erosion of the Creta- 
ceous may have occurred during Pleistocene and recent times. 
Character of the Materials Hroded. 
The character of the materials in western Kansas into which the 
different drainage channels have been eroded differs greatly in 
1 Clarence King, U. S. Geolcgical Exploration of the Fortieth Parallel, Vol. I., 
p. 451. Washington, 1878. 
