394 W: M. DAVIS 



as rain works with the wind, since the rain constantly seeks to wash 

 waste into the hollows formed by the wind, whose tendency to make 

 hollows is thereby counteracted. 1 



The verity o] the arid cycle. — The deductive method by which 

 most of the preceding paragraphs are characterized may be regarded 

 by some readers as reaching too far into the field of untestable spec- 

 ulation. It is true that the examples of observed forms, by which 

 the deduced forms of every stage should be matched, are as yet 

 not described in sufficient number; but this may be because desert 

 regions have not yet been sufficiently explored with the principles 

 herein set forth — particularly Passarge's law — in mind. On the 

 other hand, the examples of desert plains in South Africa, described 

 by Passarge as plains of the Bechuana (Betschuana) type, suffice 

 to show that the stage of widespread desert-leveling has actually 

 been reached in that region, and thus justify all the earlier stages; 

 for, however many land movements may have interrupted the regular 

 progress of preceding cycles, the occurrence of widespread rock 

 plains proves that at least the present cycle of arid erosion has been 

 long continued without disturbance. 



The levelness of the plains over wide areas is especially emphasized. 

 Isolated mountains rise above the plains; and the combination of 

 the two unlike forms is described under the term Inselberglandschajt, 

 suggested by Bornhardt. Passarge states that these desert plains 

 are not undulating with low hills, but true plains of great extent, 

 from which the isolated residual mountains rise like islands from 

 the sea. The residuals may be low mounds, only a few meters high, 

 or lofty mountain masses, rising several thousand meters above 

 the plains. The plain surrounds the steep slope of the mountains 

 with a table-like evenness; there is no transitional belt of piedmont 

 hills, and no intermediate slope (b, p. 194). The mountains consist 

 of resistant rocks, such as granite, diorite, gabbro, quartzite, etc., 



1 "Herr Geheimrath v. Richthofen machte mich auf die Schwierigkeit aufmerk- 

 sam, die riesigen, faktisch ebenen Flachen durch Windwirkung zu erklaren, dafiir 

 d;r Wind kein 'basdevel of erosion' bestande und er aus Gestein, das sich leicht 

 abtragen lasst, b?deutende Vertiefungen ausarbeiten konne und musse. Diese 

 Schwierigkeit fallt fort, sobald sptilender Regen mitarbeitet. Denn dieser sucht die 

 durch den Wind g?schaffenen Vertiefungen bestandig mit Schutt — Sand, Lehm, etc. — 

 auszufullen, arbeitet also dem Wind entgegen" (Passarge, b, p. 208). 



