474 ELEMENTARY GEOLOGY 
Quaternary Geography. — In the eastern part of the 
United States, the geographic conditions of the Qua- 
ternary were not greatly different from those of the 
present. Some small portions of the seaboard states 
were submerged; and gradually, as the Quaternary 
continued, these rose above the sea until the present 
boundary of the country was reached (p. 298). 
In the west, however, mountain growth continued, 
and with it voleanic action. The last of the western 
mountains to form were the Coast Ranges, which are 
probably even now in process of uplift, although they 
have passed the time of maximum growth. In various 
parts of the plateau region, other mountain chains were 
formed, and here also, in some places the mountain 
growth seems to be still, though slowly, in progress. 
During the Tertiary, many lakes of large size covered 
parts of the west. Some of these were destroyed 
by filling with sediment, others by having their bar- 
riers cut down by the streams that flowed out of 
them, and still others were. drained by changes in 
the level of the land, which so tilted them that the 
water was spilled out. Some of these basins, formed 
during the progress of the Cretaceous, Tertiary, and 
Quaternary mountain growth, still exist in the plateau 
and mountain country. Of these very few now con- 
tain water, and most that do are occupied by shallow 
salt pools in the lowest parts of the basins. 
