42 
MUSEUM BULLETIN NO. 11. 
sets of fault zones and sets of parallel valley stretches. The 
indication is that the valley bottoms follow the fault zones. 
The peculiar drainage pattern of the Beaverdell area is repeated 
over the rest of the plateaus, and it suggests that the same con- 
ditions hold for the plateaus as a whole. 
The difference in the topographic forms developed upon 
different rock formations of the Tertiary in the Beaverdell area 
proves a definite relationship between topography and structure 
upon those areas. In the Kamloops area such a relationship is 
indicated by the manner in which Miocene lavas, on the uplands 
near Highland valley, overlie granite. It looks as if the lava 
were acting as a protective cap to the granite. Evidences of the 
disregard of the topography of the uplands for rock structure are 
plentiful. Pre-Tertiary rocks of the Beaverdell area are planed 
across, irrespective of their structure. In the Kamloops area 
the upland cuts across Miocene lavas with a dip of 25 degrees, 
and at Tulameen across a centroclinal basin of Tertiary sedi- 
ments (Figure 2, profile 6, and Plate V). The disregard of 
topography for the structure is, therefore, the more prominent 
feature, but in some respects topographic form is evidently still 
controlled by rock structure. 
Average Regional Slope and Relative Relief, —We have pointed 
out in the regional description of the Plateaus that in their 
southern portion the average regional slopes of the uplands 
measure between 160 and 300 feet to the mile and that differences 
of elevation of 2,000 feet are of constant occurrence within 10 
miles of each other. In discussing the theory of the geographic 
cycle we have shown that land surfaces with such slopes and relief 
are more closely related to rugged mountains than to plain- 
like forms; on the basis of that theory, therefore, the uplands 
of the Interior plateaus represent a stage closer to early maturity 
than to old age. 
To Sum Up : — The number of local irregularities of slope, 
that is, cliffs and flat areas which are to be found on the upland 
together with the partial accordance which exists between its 
topographic form and rock structure, proves that it represents 
a stage of development between early maturity and old age. 
The average grade of its slopes and general relief show that the 
