EQUIPLANATION 



347 



allowed to continue undisturbed sufficiently long will include the re- 

 siduals. Stream action and other destructive forces are, however, alsq 

 engaged in destroying the uplands, and tend ultimately to again bring 

 the district to a peneplanated or old-age condition. 



In numerous places in the upland angular blocks of limestone, 1 to 3 

 feet in thickness, were noted projecting through the soil and fine waste, 

 having been torn from the underlying bedrock and heaved into this posi- 

 tion by frost action. These blocks gradually decompose, and in so doing 

 contribute to the superficial materials of the upland, which in places 

 resemble slacked lime, and occasionally are not unlike marl; but where 

 the calcareous ingredients have been largely removed and only the im- 

 purities of the limestones remain, a rather typical soil or clay is exhibited. 

 In places calcareous precipitates were also noted, which are being de- 

 posited from waters that are leaching the rocks elsewhere. 



The processes just described are not thought to be limited to the one 

 district here mentioned, but are believed to occur extensively in various 

 Arctic regions. In addition, however, in many other districts and coun- 

 tries, sets of forces and processes quite different from these may cause 

 equiplanation. In official reports on parts of southern Yukon^ and 

 northern British Columbia,'^ included in the Yukon plateau, the writer 

 has described a similar process, although without naming it, which is 

 attributable largely to nivation, and is causing portions of the upland 

 there to become more and more plainlike. Also in many mountainous 

 areas having interior drainage, plainlike surfaces tend to be produced by 

 the double process of wearing down the i-anges and filling up the basins. ^^ 



The plains thus formed will consist partly of worn-down rock and 

 partly of built-up waste, and in their process of construction no gain or 

 loss of material is involved. The mean levels of many such areas are 

 slowly reduced by wind action, which exports, annually, varying amounts 

 of material; but under certain conditions there is no export of material, 

 and even when this occurs the equiplanation acts quite independently 

 of the exporting process. 



The equiplanating process, here described as occurring in northern 



^ D. D. Cairnes : "Wheaton River district." Geo). Surv.. Department of Mines. Canada 

 (in press). 



» D. D. Cairnes : "Atlin mining district." Geol. Surv.. Department of Mines, Canada 

 (in press). 

 1" J. Walther : "Das Gesetz der Wustenbildung." Berlin, 1900. 

 E. Passarge : "Die Kalahari." Berlin, 1904. 



A, Tenck : "Einfluss des Klinas auf die Gestalt der Erdoberflache." 

 W. W^ Davis : "The geographic cycle in an arid climate." Tour, of Geol., July- 

 August, 1905. 



