38 
MUSEUM BULLETIN NO. 11. 
The period following was evidently one of degradation of the 
land, for at the time the lavas were laid down a mature surface 
had been developed. The relative relief within the Beaverdell 
area was more than 1,500 feet, and the drainage lines occupied 
approximately the same position as they do to-day. The 
evidence of the relief is furnished by the actual contacts of 
the lavas with the underlying rocks. Thus in Nipple moun- 
tain this contact varies from 3,500 to 4,800 feet above sea- 
level. On Cranberry ridge it is 4,500 feet, and on Wallace 
mountain about 5 miles to the southeast between 5,000 
and 5,400 feet. At Lassie lake it is 4,300 feet, and 3 
or 4 miles to the northeast in the bottom of Kettle valley it 
lies between 2,500 and 2,800 feet. Although there has been 
folding of the lavas since, it is not probable that they have 
shifted very greatly in a vertical direction. It may, therefore, 
be supposed that the relative relief within the quadrangle was 
at least 1,500 feet. The tilting of the contact surfaces from the 
Nipple and the China buttes toward the West Fork valley sug- 
gests a depression in that direction, and the finding of lavas 
upon the present bottom of the Kettle river near Copper creek 
suggests an old valley there. Such is the evidence in regard 
to the former drainage. The evidence for the maturity of the 
topography is that the topography developed upon rocks older 
than the lavas seems much further advanced than that developed 
on the lavas themselves, and suggests that they were laid down 
upon a surface already well truncated. 
Having established the probable land form upon which the 
lavas were laid down, in the Beaverdell area, we may pass on to 
the next period. 
THE PERIOD ENDING AT THE GREAT UPLIFT. 
From the difference in composition of the lavas seen in the 
Beaverdell quadrangle, it is inferred that there at least they were 
local in their distribution ; that is, the material derived from one 
particular centre of disturbance did not cover a very extensive 
area. One may suppose that when the disturbances were over, 
certain valleys were filled up and hills of lava existed in other 
