26 CHARLES RK. KEVES 
The principles of water-action in the normal humid lands are applied 
with the only reservation that there is somewhat less water involved. 
No distinction is made between the efficiency of water-action on the 
plain and in the mountain. On the plains, with the exception of the 
local and sporadic flood-sheet, the general effect of water as a corrad- 
ing agent is practically mil. A very large part of what rainfall occurs 
on the plains sinks at once into the ground. On the mountains where 
the general erosion effects have been chiefly observed the results are 
not so very unlike what they are in the humid regions generally. 
By all those who, with the idea of genesis in mind, have recently 
traversed the region, it is conceded that erosion has had much to do 
with giving to the desert country its present topographic expression. 
That the erosion is not chiefly water-erosion but mainly eolian in 
character is an aspect of the subject which has received but scant 
attention. The potency of wind-scour as an erosive agent under 
conditions of dry climate is amply shown in many ways, and to an 
extent heretofore unsuspected. Its grander effects as compared 
with those of water corrasion are quite distinctive. Among them 
none is more characteristic than the beveled rock-floor which the 
intermont plains of the arid region present, as fully described in detail 
in another place.t Its real significance as indicating that these plains 
are areas of marked degradation instead of aggredation, as commonly 
supposed, is here especially pointed out. ‘The vastness and evenness 
of the intermont plains have no known counterpart among the plains 
of the humid regions. Desert plains are smoother than peneplains 
possibly can be, as Passarge has stated. ‘The singular isolation of 
the desert ranges, for they are usually completely encompassed by 
plains as by the sea, the entire absence of foothills, the plains-char- 
acter of the rock-floor itself,? the representation of former plains- 
levels by the plateau-plains, the remarkable thinness of the surface 
mantle of débris, the total absence of distinct water-ways on the 
plains,3 the notable independence of, and marked differences in, level 
of contiguous plains, and the general tectonic characters,+ are inex- 
t Am. Jour. Sci. (4), XV, p. 207, 1903; also Bull. Geol. Soc. America, XIX, p. 86, 
1908. 
2 Eng. and Min. Jour., UXVIII, p. 670, 1904. 
3 American Geologist, XXXIV, p. 160, 1904. 
4U. S. Geol. Sur., Water Sup. Pap. No. 123, 1905. 
