44 
MUSEUM BULLETIN NO. 11. 
parison with the results effected in valley cutting during the 
samef period of time. 
After the beginning of the uplift there was a period of glaci- 
ation, and after glaciation ceased, a period of adjustment of the 
drainage disorganized during glacial time, and of modification 
of the topographic forms left by the glaciers. The adjustment 
and modification have continued until the present time. 
Glaciation. 
Glaciation occurred first by means of a continental ice 
sheet which moved southerly over the Interior plateaus and 
east of south in the Beaverdell area; and later, after the ice sheet 
had disappeared, by valley glaciers which moved down the 
larger valleys. 
Evidence of the continental ice sheet consists of striae, 
with a constant general trend to the southeast, which occur upon 
the higher ridges, and of the blanket of drift which is found all 
over the uplands. From the evidence of transported boulders 
sometimes striated and generally smooth, which are found on 
points like Nipple mountain at an elevation of 5,758 feet, and 
on King Solomon mountain at 3,800 feet, we may conclude that 
the ice sheet was quite thick, probably at least 2,000 feet. 
The ice sheet carved out rock basins in which lakes now 
exist, and probably scraped away most of the residual soil from 
the rock surfaces. It deposited drift, which dammed up streams 
and often diverted their waters. A great number of the swampy 
areas on the Beaverdell uplands are undoubtedly the result of 
glacial damming of streams. Some of the lakes are also due 
to this, while others are partly or wholly hollow basins carved by 
the glaciers in bedrock. Evidences of alterations of drainage 
due to the continental ice sheet are many; they are referred to 
again under “Stream Piracy." 
After the ice sheet had disappeared from the Beaverdell 
area there was a further invasion of valley glaciers which scoured 
out certain of the valleys and deposited glacial debris upon 
their retreat. How many periods of valley glaciation there 
were we do not know. From their shape we conclude that the 
