34 University Geological Survey of Kansas. 
large amount of sediment from the hills and valley slopes to the 
lower levels, where it is deposited. The river is now said to be 
in a stage of maturity. 
The divides are cut down more and more until the old plateau 
comes nearer and nearer to asmooth plain of much lower level, 
the plane of erosion or base level. ‘The velocity of the stream 
becomes less and less; the river does very little work of ero- 
sion, and it has now entered the period of old age. When the 
river bed finally is at the level of the sea the current is stopped 
and the river is dead. 
Such a history comprises the theoretical cycle of a river and 
through it every river will pass in the course of time. A very 
long time may be taken for this cycle and as yet probably no 
river has ever passed through it, for our land is nowhere very 
old since its last elevation. Our rivers over the land are in vari- 
ous parts of the cycle. 
When the history of rivers is carefully studied it is found to 
be much more complex than the outline given, for movements 
of elevation of the land may throw the period in the cycle of a 
river back again to an earlier one; or movements of depression 
may change the period to a later portion of the cycle. ‘The va- 
riations which complicate the history need not be mentioned in 
this place, but enough has been given to show that the topog- 
raphy or relief of the land is dependent for the most part on 
river development and the accompanying forces of the atmos- 
phere. 
With the general history of river development in mind, we 
will see how far it applies to the development of the topography 
of the region now under discussion. 
TOPOGRAPHY OF NORTHERN OR BLUE RAPIDS AREA. 
The phrase ‘‘low, monotonous prairies of Kansas’’ has no ap- 
plication to the gypsum belt, for there this feature is entirely 
absent. The northern area, Plate II, is a dissected plateau, of 
about 1300 feet elevation,” which is now so indented by the Big 
Blue and Little Blue rivers, with their smaller tributaries, as to 
_ 15. Elevations in this paper are taken from the United States Geological Survey topougraph- 
ical maps of Kansas. 
