PHYSIOGRAPHY OF THE BBAVERDBLL MAP- AREA. 
41 
The Uplands in the Stage of Late Maturity . 
The evidence given above, coupled with a study of a number 
of profiles in the Beaverdell and Tulameen area (see Figure 2, 
profiles 1 to 6), have led us to believe that no interruption of the 
cycle took place between the laying down of the lavas and the 
great uplift. It still remains to prove that at the uplift the 
uplands had reached the stage of late maturity. Late maturity 
is the stage between early maturity and old age. In early 
maturity the topography is rugged, cliffs are plentiful on the hill 
sides, and there is a definite relation between topography and 
rock structure. In old age the relative relief is very low, cliffs 
are scarce or wanting, the soil covering is heavy, and there is no 
relation between the topography and the structure of the under- 
lying rocks. 
The hypothesis that the cycle had attained the stage of 
late maturity is based upon the presence of cliffs and other 
local irregularities of slope, the partial accordance which exists 
between topography and structure, and the degree of average 
regional slope and relative relief which exists on the uplands. 
Local Inequalities of Slope.— On pages 22 and 23 we have 
given evidences of the presence of cliffs and flat areas upon the 
uplands in the Beaverdell area, which vary markedly from the 
average regional slope. Some of them occur far away from the 
present deep canyons, and could not have been formed from 
erosion subsequent to the uplift. They occur at all angles to 
the prevailing southeasterly movement of the continental ice 
sheet, and many of them could not have been formed by glacial 
plucking. A good many cliffs, short, steep slopes, and also 
flat areas must, therefore, have existed upon the uplands at the 
time of the great uplift. 
Partial Accordance between Structure and Relief. — In the 
description of the Beaverdell map-area, and of the Interior 
plateaus as a whole, we have discussed at some length the rela- 
tionships between the upland topography and the rocks under- 
lying it. Near Beaverdell the river valleys consist of straight 
stretches, and straight stretches in adjacent valleys are paral- 
lel. A relationship evidently exists between the direction of 
