PHYSIOGRAPHY OP THE BEAVERDELL MAP-AREA. 33 
4 
GLACIAL FORMS. 
A few topographic forms occur in sheltered parts of the 
valleys which are typical of glacial deposits, and some irregular 
mounds and ridges are found which have the appearance of 
somewhat modified glacial deposits. In Wallace draw both 
lateral and end moraines occur. Here a long narrow ridge 
follows for some distance along the foot of the Knob Hill side of 
the draw, and another, below it, lies two-thirds of the way 
across the valley. These ridges are about 30 feet wide on top 
and slope smoothly away to both sides at angles of about 20 
degrees. The top of the lateral moraine along the hill side is 
about 60 feet above the adjacent valley floor and pitches with 
some irregularities down the valley. Between it and the foot 
of the hill is a draw about 20 feet deep. The slopes along this 
ridge top are remarkably smooth. Below the cross ridge there 
is a jumble of irregular mounds and depressions in which drainage 
lines are absent or only feebly developed. The cross ridge and 
the mounds below it form the end moraine. Such glacial forms 
are comparatively rare in the Beaverdell quadrangle and can be 
looked upon more as accessories than essential parts of the 
topographic surface. 
GENESIS OF THE PLATEAU TOPOGRAPHY. 
In order to obtain a basis upon which to classify the land 
forms found in the southern Interior plateaus we shall begin this 
section by a discussion of the theory of the geographic cycle, 
and will give reasons for believing that a classification of land 
forms according to their average regional slopes is desirable 
and necessary. The discussion is followed by an account of 
the physiographic development of the plateaus. 
The Geographic Cycle. 
According to the prevailing theory of physiographic develop- 
ment, if a portion of the earth’s crust be raised a certain amount 
above sea-level the atmospheric agencies of disintegration, decay, 
