440 A JOURNEY IN BRAZIL. 
glaciers, part to the icebergs and to freshets consequent on 
their breaking up, they will find that they have covered 
the whole ground, and that the two theories are perfectly 
consistent with each other. I think the present disputes 
upon this subject will end somewhat like those which di- 
vided the Neptunic and Plutonic schools of geologists in 
the early part of this century ; the former of whom would 
have it that all the rocks were due to the action of water, 
the latter that they were wholly due to the action of fire. 
The problem was solved, and harmony restored, when it 
was found that both elements have been equally at work 
in forming the solid crust of the globe. To the stranded 
icebergs alluded to above, I have no doubt, is to be re- 
ferred the origin of the many lakes without outlets ex- 
isting all over the sandy tract along our coast, of which 
Cape Cod forms a part. Not only the formation of these 
lakes, but also that of our salt marshes and cranberry- 
fields, I believe to be connected with the waning of the 
ice period. 
I hope at some future time to publish in detail, with 
the appropriate maps and illustrations, my observations 
upon the changes of our coast, and other phenomena con- 
nected with the close of the glacial epoch in the United 
States. To give results without an account of the investi- 
gations which have led to them, inverts the true method 
of science ; and I should not have introduced the subject 
here except to show that the fresh-water denudations and 
the oceanic encroachments which have formed the Amazo- 
nian Valley, with its river system, are not isolated facts, 
but that the process has been the same in both continents. 
The extraordinary continuity and uniformity of the Ama- 
zonian deposits are due to the immense size of the basin 
