472 ELEMENTARY GEOLOGY 
square miles of western plateau are covered with the 
lava which has been erupted from these vents. 
In the eastern part of the country, the seaboaid 
states were still partly below the sea-level at the begin- 
ning of the Tertiary period. As a result of this, beds of 
marine deposits were laid down over the eastern border 
of the states south of New Jersey. Long-continued 
denudation had lowered the remaining part of the east- 
ern states to a lowland condition. Even the mountains 
were greatly reduced in elevation. Then followed an 
uplift, which brought not only the eastern part of the 
country above sea-level, but also elevated the sea bot- 
tom, which lay off the shore, to a condition of dry 
land. This uplift raised the land and sea bottom to 
a height, which in New England was certainly not less 
than one thousand feet above the present. 
The evidence of this is of two kinds. In the first place, the 
coast of New England and of Canada is entered by the sea in 
the form of numerous bays and fjords. These bays, such as the 
St. Lawrence, are seen to be perfect river valleys whose ends are 
partly beneath the sea. Such is the case, for instance, with the 
Hudson, Delaware, Chesapeake, and the thousands of smaller 
bays upon the eastern coast. The second evidence is found upon 
the bottom of the sea. Soundings made there have revealed the 
fact that off the mouths of some rivers, such as the St. Lawrence 
and Hudson, there are distinct channels cut into the bottom, and 
extending from the present mouth of the river to the edge of the 
shelf which borders the continent (Fig. 181). These have every 
appearance of being river valleys; and if so, they must have 
a Fa 
