PLANATION INDEPENDENT OF SEA LEVEL 77 



[exicoT It was an easy matter to fancy that under the abnormal condi- 

 tions of an arid climate and through means of eolian and sheetflood ero- 

 sion local planation of the intermont areas might not only take place, but 

 that the process might be general in character, notwithstanding the fact 

 that the general plain thus formed was high above baselevel. 



The idea became fixed by the proposal of a title meaning a surface of 

 general planation of the earth, whether near baselevel in humid regions, 

 far above baselevel in the dry lands, or below baselevel in the case of 

 marine denudation. A new and distinct name for the surface of general 

 planation in arid regions alone seemed inadvisable, especially since in 

 southwestern United States such a plain merged on the one hand into a 

 true peneplain and on the other into raised marine plains. It was 

 thought for a while that the meaning of peneplain could be extended so 

 as to cover the new field, and in this sense that title was actually used a 

 number of times before abandonment. On account of these and some 

 other "heresies," which have since been thoroughly substantiated, the 

 full report on the Estancia plains was greatly dela5red in publication, and 

 finally rejected by the United States Geological Survey. 



In the meanwhile appeared Passarge's important memoirs on the 

 "Rumpfllache und Inselberge"^^ and "Die Inselgeberglandschaft im 

 tropischen Afrika"^® bearing on the same subject. Passarge, in the 

 South African field, had greatly the advantage of the geologists who had 

 visited the western American regions, in that he had to deal with a high 

 desert region in the topographic stage of old age, and a region long undis- 

 turbed by mountain-making forces, instead of a country traversed by 

 several large streams flowing through to the ocean, disturbed very re- 

 cently and very profoundly and intricately cut up into huge blocks Avhich 

 have the appearance of earliest youth. 



Passarge's conception is briefly and essentially this: That in the geo- 

 graphic development of the South African region there is finally a stage 

 reached in which an elevated plain, under an arid climate, is reduced to 

 a lower and evener surface chiefly through the blowing away of the fine 

 materials, though aided occasionally by sheetflood, leaving a beveled rock- 

 floor only thinly covered by ordinary soft deposits and having no rela- 

 tionship to the baselevel of erosion as commonly understood. To all 

 intents, such a plain is a typical peneplain, wholly unrelated to the sea- 

 level. Davis" well says that we may regard this generalization as sec- 

 ondary only to Powell's generalization concerning the general baselevel of 

 erosion. 



1= Zeitschrift der dentsche geologische Gesellschaft, Ivi band, Protokol, 1904, pp. 193- 

 209. 



" Natnrwiss. Wochenschr., new series, iii band, 1905, pp. 657-665. 

 " Journal of Geology, vol. xiii, 1905, p. 373. 



