22 W. M. DAVIS 



The arid cycle is least developed; its theoretical aspects have 

 been carried far beyond their confirmation by observation; not 

 that observation in deserts is wanting, but that the observers 

 there have usually failed to test the correctness of the expectations 

 to which the deductive discussion of this special cycle have led/ 

 Walther's studies of deserts are as a rule more concerned with the 

 actual processes there at work and the forms that they immediately 

 produce rather than with the place of such processes and forms in 

 the whole sequence of inferred forms that constitutes a complete 

 cycle of arid erosion. Certain phases of the arid cycle have, 

 however, been admirably analyzed with respect to actual features 

 in the desert region of the southwestern United States by Lawson^ 

 and Bryan.3 In all its aspects, the scheme of the erosion cycle 

 has grown by degrees, sometimes slowly, sometimes rapidly; and 

 its growth is still going on, partly by the correction, partly by the 

 modification and extension of earlier ideas. 



Reception of the scheme of the erosion cycle. — With many of the 

 older physiographers and geologists in the United States today, 

 whose individual development in their science has been contempo- 

 raneous with the growth and establishment of the scheme of the 

 cycle of erosion, its use has been an every day affair, and its advance 

 has been a part of their own progress; but they have often made 

 more use of its principles than of its terminology. Among the 

 younger ones, the scheme has been very largely accepted, ready 

 made, from their seniors. But a few reservations are here needed: 

 for example, the term subsequent, defined as above, has been seldom 

 employed, in spite of the very frequent occurrence of subsequent 

 rivers and valleys in regions of deformed strata; it has been replaced 

 by paraphrases. Other terms, such as obsequent and resequent, 



' Since writing the statement above, a paper by E. Kaiser, of Munich, on "Morpho- 

 genetische Ergebnisse auf Reisen wahrend des Krieges in Siidwestafrika" (Verh. 20, 

 Dentschen Geographentages [Leipzig, 1921], pp. 159-75) has been received, in which 

 it is said that the observed forms of the coastal desert near Liideritz Bay confirm 

 certain of the deduced forms of the arid cycle (see p. 175). 



= "The Epigene Profiles of the Desert," Cal. Univ. Dept. Geol. Bull., Vol. IX 

 (1915), PP- 23-48. 



3 "Erosion and Sedimentation in the Papago Coimtry, Arizona," U.S. Geol. 

 Surv., Bull. 730 B, 1922. 



