82 Cairnes — Some Suggested New Physiographic Terms. 



The process of equiplanation in regions having interior 

 drainage has been described (without specific use of the term 

 here proposed) by Walther,* Passarge,f Pcnck,;):, Davis,§ and 

 practically all recent writers of note who have dealt with 

 desert lands. Professor Davisf writes: "There is no novelty 

 in the idea that a mountainous region of interior drainage may 

 be reduced to a plain by the double process of wearing down 

 the ranges and filling up the basins, and that the plain thus 

 formed, consisting partly of worn-down rock and partly built- 

 up waste, will not stand in any definite relation to the general 

 base-level of the ocean surface." 



As deserts commonly have interior drainage, and since the 

 arid deserts of the globe, according to Sir John Murray,! 

 cover over a fifth of its land surface, the vast importance of 

 this process can be readily appreciated. 



Equiplanation is thus mainly active in regions subjected to 

 an arctic or an arid or semi-arid climate. However, nivation 

 or snow-drift action has been noted to have an equiplanating 

 effect in other localities. Matthes** has shown that in the 

 Bighorn mountains, nivation tones down the features of the 

 upland by the production of great quantities of mud which 

 tends to fill the depressions in this surface. During seasons 

 when the snow on the upland surface is reduced to occasional 

 drifts, the ground in front of the drifts is kept continually 

 moist by melting of the snow in the daytime. The water 

 penetrates into every crevice of the underlying rock which 

 becomes much broken and comminuted at night or on colder 

 days when the water freezes. This excessive frost action about 

 the receding margins of the drifts during certain seasons of 

 the year produces a great amount of fine material which is 

 carried away by the innumerable rills of water trickling from 

 the edge of the snow, and lodges in the nearest slight depres- 

 sion. 



In northern British Coluinhiaff and southern Yukon, ty the 



* Walther, J., "Das Gesetz der Wustenbildung," Berlin, 1900. 



•f- Passarge, E., "Die Kalahari," Berlin, 1904. 



X Penck, A., "Einfiuss des Kliinas auf die Gestaltder Erdoberfiache," 1883. 



§ Davis, "The geographic cycle in an arid climate," Jour, of Geol., July- 

 Aug., 1905. 



|| Davis, W. M., "Geographical essays," p. 304. 



IT Murray, Sir John, "Origin and character of the Sahara"; Science, 

 vol. xvi, 1890, p. 106. 



** Matthes, F. E., "Glacial sculpture of the Bighorn Mts., Wyo.," 

 Twenty-first Ann. Rep., U. S. Geol. Surv., Pt. II, 1899, pp. 173-190. 



ft Cairnes, D. D., "Portions of Atlin district, B. C," Sum. Rep., Geol. 

 Surv. Dept. of Mines, Can., 1910, p. 29 ; idem., "Atlin Mining district, B.C.," 

 Memoir Geol. Surv., Dept. of MiDes, Can. (in press.) 



XX "Wheaton River district, Yukon," Memoir Geol. Surv., Dept. of 

 Mines, Can. (in press.) 



