326 J. D. Dana on American Geological History. 
Much doubt must remain about the origin of the drift, until 
the courses of the stones and scratches about mountain ridges 
and valleys shall have been exactly ascertained. The general 
course from the north is admitted; but the special facts proving 
or disproving a degree of dependence on the configuration of the 
land have not yet been sufficiently studied. 
One theory, the most prevalent, supposes a deep submergence 
over New England and the North and West, even to a depth of 
four or five thousand feet, and conceives of icebergs as floating 
along the blocks of stone, and at bottom scratching the rocks. 
Another, that of the Professors Rogers, objects to such a sub- 
mergence, and attributes the result to an incursion of the ocean 
from the north, in consequence of an earthquake movement 
beneath the Arctic Seas, 
The idea of a submergence is objected to on the ground that 
the sea has left no proof of its presence by fossils, sea-shore ter- 
races or beaches. 
v7 ee 
farther south; and yet no such sea-shore marks now exist to 
shore recor 
Very many have replied in the affirmative; and one able ad- 
vocate of this view, who sees no difficulty in the total absence 
of sea-shore terraces or fossils at all levels above the Laurentian 
beds, finds in the succeeding epoch sea-shore accumulations in 
all the terraces of our rivers. Why this wonderful contrast? 
What withheld the waves from acting like waves in the former 
case, and gave unbounded license in the latter? 
‘This much, then, seems plain, that the evidence although neg 
ative, 1s very much like positive proof that the land was not 
beneath the sea to the extent the explanation of the drift phe- 
nomena would require, . 
There are other objections to this view of submergence. If 
North America were submerged from the southern boundary-line 
much warmer climate for the continent than now; if only half- 
way, then there is another east-and-west shore line to be trac 
out, before the fact of the submergence can be admitted. Again, 
heres Us 
