3 6 
MUSEUM BULLETIN NO. 11. 
referred to as peneplains. 1 * * The same name is applied to the 
Laurentian plateau 4 5 and the Great plains of western Canada* 
which have average slopes of less than 10 feet per mile, and are 
really plain-like in appearance. Not only do the uplands not 
resemble plains, but, according to the idea of extreme slowness 
in the later stages of the degradation of the land forms, 4 they 
are further removed in time from land surfaces with slopes of 
10 feet to the mile than from rugged mountains with slopes of 
from 800 to 2,500 feet to the mile. The necessity of defining 
the relief of various land forms becomes more apparent when 
remnants of an old land surface are used to measure earth- 
warping by. Here the accuracy of measurement is directly re- 
lated to the amount of original relief, and that relief is often 
disregarded. 6 For instance, if the original surface has a relief of 
1,000 feet, the measurements of warping upon isolated remnants 
of that surface are, of course, apt to be out by 1,000 feet. 
We may conclude then, that a classification of this type 
is desirable and necessary, and that it would not be contrary 
to the existing theories of the development of land forms. In 
the following account of the physiographic development of the 
Interior plateaus the criterion of regional slopes, or relative 
relief, is used as the chief basis for classifying the land forms 
found therein. 
Physiographic Development. 
In the following account of the physiographic development 
conclusions are largely drawn from a study of the Beaverdell 
map-area. Since, however, the topography of this area is very 
similar in drainage pattern and relief to mapped areas in the 
^‘Report on the area of the Kamloops map-sheet, British Columbia," 
by G. M. Dawson, Geol. Surv., Can. Ann. Rep., Vol. VII, part B, pp. 4-5. 
*"The Laurentian Peneplain," by A. W. G. Wilson, Jour. Geol,, Vol, XI, 
1903, pp. 628-629. 
*“Forest Physiography" by Isaiah Bowman, pp. 410-411, New York, 
1911. 
4 “The Geographic Cycle," by W. M. Davis, Geographic Journal, Vol. 
XIV, 1899, p. 486. 
5 "An old erosion surface in Idaho: a criticism," by Eliot Black welder, 
Jour. Geol., Vol. XX, No. 5, July-August, 1912, pp. 410-414. 
