PHYSIOGRAPHY OF THE BEAVERDELL MAP-AREA. 
39 
places. It is quite possible that parts of the original surface 
were never covered with lava. The present uplands were de- 
veloped from the partly or wholly lava covered land surface. 
The method of that development must be deduced from what we 
know of the uplands to-day. It is here assumed that, except 
where dissected by streams, they have changed very slightly in 
character since the “great uplift." 
Two alternative hypotheses are advanced here to account for 
the present form of the uplands. The first is that it is a pene- 
plain which may or may not have been somewhat dissected 
before the great uplift took place; the second hypothesis is to 
the effect that the uplands represent a land form in the stage of 
late maturity and that there are no evidences of the interruption 
of the cycle between the laying down of the lavas and the great 
uplift. 
The Presence or Absence of Peneplain Remnants. 
The tenability of the first hypothesis depends upon the 
finding of peneplain remnants which were formed after the de- 
position of the lavas and before the great uplift. The arguments 
for peneplanation are first of all the general evenness of skyline 
to be observed in all parts of the plateaus, and in the second 
place the fact that the greater part of the upland surface cuts 
indiscriminately across rocks of different formations. 
Flatness of skylines would indicate that upon the higher 
ridges remnants were left of what was once a fairly flat surface. 
This argument is strengthened if a number of ridge tops lie at an 
elevation close to that of some of these flat crestllnes. In the 
Beaverdell quadrangle there are a number of such ridge tops lying 
at elevations of between 4,500 and 4,800 feet, and some of them 
have apparently quite flat skylines. That flatness of skyline is 
not a very safe criterion for the determination of plain or pene- 
plain remnants, is indicated by the fact that such even crestlines 
occur at elevations 700 feet apart and only 2 or 3 miles away from 
each other in several places in the Beaverdell quadrangle. Thus 
the observer by climbing up the side of the West Fork valley 
near Hall creek and looking east would first see a flat skyline 
