THE 



JOURNAL OF GEOLOGY 



JULY-AUGUST, 1905 



THE GEOGRAPHICAL CYCLE IN AN ARID CLIMATE 



W. M. DAVIS 



Normal and special cycles. — The scheme of the geographical cycle 

 is usually developed with respect to a land surface under ordinary 

 climatic conditions, not so dry but what all basins overflow and all 

 parts of the surface have continuous drainage to the sea, nor so cold 

 but what the snow of winter all disappears in summer. The term 

 "normal climate" has been applied to such conditions, and "normal 

 cycle" to the scheme that embodies them. It is chiefly this scheme 

 that I have elsewhere treated on various occasions {a, b, c, h). 1 



The general scheme of the geographical cycle needs adaptation to 

 two special climates: one, glacial; the other, arid. The glacial cycle 

 received brief attention in one of my papers (d) five years ago, but 

 now needs supplement in view of the later studies by Richter, de 

 Martonne, Lawson, and others, as to the forms of glaciated mountains, 

 and in view of the theory announced by Gilbert that glaciers are not 

 buoyed up while they rest on the sea bottom, and that they may 

 therefore erode their channels deep below sea-level. The arid cycle 

 has not been considered as a whole, although special studies of desert 

 conditions have been made by various observers, notably by Walther. 

 The following general considerations are based on the work of others 

 as well as on my own observations in the arid regions of the western 

 United States and of western Asia; they are presented for the most 



1 See list of references at the end of this article. 

 Vol. XIII, No. 5 381 



