554 C. R. KEYES THE GEOGRAPHIC CYCLE IK AN ARID CLIMATE 



is not comparable to the water action of moist climates, but that it is as 

 idle as the shifting by the winds of the sands of the seashore. The finer 

 rock-waste disturbed by these agencies is soon borne away by the winds 

 as other soils of the desert. On the evaporation of the broad, thin sheet 

 of storm waters producing playas the bottom muds curl up in thin leaves 

 and are blown away. Playas and similar mud-flats of the arid basins 

 must be considered as areas of rapid denudation and only temporary 

 areas of relatively inconsequential aggradation.^^ 



That subsequent streams in a strictly arid region have so small a 

 chance for development does not appear to be due so much to the fact 

 that the weak substructure of the interment plains is deeply covered by 

 waste as it is to the more obvious fact that there is not sufficient rainfall 

 to form such streams. 



Mature Stage of arid Eelief 

 deductive course of development 



In the modification of the normal geographic cycle to meet the new con- 

 ditions imposed by an arid climate, several features are especially note- 

 worthy. For the mature stage it is postulated that the continued erosion 

 of the highlands and divides and the continued deposition in the basins 

 produce a coalescence of local drainage systems, headwater erosion of 

 consequent and subsequent streams, and aggradation of higher basins 

 favoring this change; that a beginning is made of the confiuence and 

 integration of drainage lines which, when fully developed, characterize 

 maturity ; that when the drainage established across a former divide has 

 a strong fall an impulse of revival and deeper erosion makes its way 

 across the aggraded floor of the higher basin, which becomes dissected 

 with bad-land expression; that this dissected floor then is smoothed at a 

 lower level, and that in the last mentioned case the large areas of rock- 

 floor are laid bare. Wind action is given a very subordinate place. In 

 support of these distant deductions I have never found any evidence. 



MATURE ARID FEATURES UNDER DEFLATION 



The strongest contrast between the mature relief characteristics of 

 normally moist lands and those of the desert under the influences of arid 

 climate lies in the complete adjustment of consequent and subsequent 

 streamways in the one case and the total absence in the other. The 

 drainage integration which the moist country normally undergoes finds 

 in arid lands no such intricate counterpart. 



Bull. Geol. Soc. America, vol. 19, 1908, p. 84. 



