AKID CYCLE IN A MOUNTAINOUS REGION 589 



scheme, corresponding in its several phases to those of the normal cycle, 

 must be very rare indeed. The prevailing mode of desert leveling and 

 lowering of an arid country must be after the fashion described for the 

 South African region. The latter would then represent the general 

 course of desert-leveling without marked stages rather than only the 

 senile stage, as has been argued. 



ARID CYCLE IN A MOUNTAINOUS REGION 



When critically examined in the light of well known arid conditions, 

 rather than measured by the standards of a moist climate, the evolution 

 of a distinctly staged arid cycle beginning with mountainous relief, as 

 outlined by Davis, is found to be merely the normally wet cycle recast 

 with somewhat less water. The sequence of events described might extend 

 under certain circumstances to an area of semi-arid character where both 

 wind and water struggle for erosional supremacy, but it does not seem 

 possible that it could obtain in a strictly desert region or a country where 

 there is an annual rainfall below 10 inches. Moreover, the scheme men- 

 tioned postulates stream action as the chief erosive agency, while wind 

 scour is considered only incidentally. The very reverse would seem to 

 be true if we are to place any reliance whatever on the accounts of those 

 who have dwelt in the desert country for any considerable length of 

 time. In a country having the small annual precipitation mentioned, 

 nineteen-twentieths of which sinks as soon as it touches it and does not 

 appear as stream water at all, it is exceedingly difficult to understand 

 how water can have the same or greater erosive efficiency that it does in 

 a humid land. 



In the Davis scheme the several stages of arid relief development do 

 not seem to be very sharply demarked. If the periods of infancy, youth, 

 and maturity could be distinctly made out in t5rpical desert regions, as 

 they are outlined, and paralleled with the wet C3^cle stages, their time 

 span would be so brief and unimportant, compared with the duration of 

 the so-called characteristics of old age, that they are altogether neg- 

 ligible, even when taking into account the boldest mountain relief. Be- 

 ginning with a plains surface, which is not unlikely the initial character 

 of most arid regions, such recognizable periods surely would be entirely 

 out of question. If it be postulated that the essential characteristics of 

 the present desert mountains of western United States, for example, are 

 comparatively recent features, and that they were mainly fashioned sub- 

 sequent to the introduction of a dry climate, as now seems altogether 

 likely, the earlier stages of the arid period must have been very different 

 from those depicted. 



