404 W. M. DAVIS 



should be transmitted to the other. It would be far otherwise if 

 the description of a desert region were undertaken systematically 

 in view of what seems to be the essential sequence of changes in all 

 deserts; that is, if the mountains and basins, the rock plains and 

 waste plains, the stream channels, the playas and the lakes, were 

 all treated in view of their place in the cycle of changes through which 

 they must be running. It is chiefly as an aid to observation and 

 record, and as an aid to the understanding of observations thus 

 recorded, that the scheme of the arid cycle may come to be of service. 



It would be fitting to accompany an article of this kind with a 

 larger number of actual examples than have been here introduced; but 

 in the endeavor to find appropriate examples, the interpretation of 

 the observations of various writers in view of the scheme here sub- 

 mitted has not seemed safe enough to make it worth while to under- 

 take it. Safe interpretation needs the conscious application of the 

 scheme by the observer in the field. When thus applied, it is to be 

 hoped that the scheme of the arid cycle may lead to the detection 

 of many facts concerning the evolution of land forms in desert regions 

 that have thus far escaped notice. In the meantime, the scheme 

 must remain in great part speculative. 



The bearing of the arid cycle on theories of elevation and depression. 

 — There is another aspect of the case which, to my mind, not only 

 gives sufficient justification for all the speculation here presented, 

 but makes one regret that it was not undertaken sooner; for in that 

 case certain theoretical discussions would have earlier gained a firm 

 foundation. 



In a recent discussion of "The Bearing of Physiography on Suess' 

 Theories" (/), I have urged that the occurrence of high-standing 

 and isolated peneplains could not be the result of the depression of 

 the surrounding lands — as is advocated by Suess — unless all the oceans 

 and their associated lowlands on other continents were also depressed 

 at the same time and by the same amount. The necessity of accepting 

 world-wide crustal movements may, however, be avoided, if the 

 high-standing truncated uplands are regarded as the result of local 

 uplifts of formerly low-standing peneplains. This alternative con- 

 clusion is so simple and economical that it is accepted by many 

 geologists and geographers; and it seems well based as long as one 



