VALLEY OF THE AMAZONS. 
225 
the ocean, the encroachment of the sea gave 
rise, not only to our large estuaries, hut also 
to the sounds and deep bays forming the most 
prominent indentations of the continental coast, 
such as the Bay of Fundy, Massachusetts Bay, 
Long Island Sound, and others. The unmis¬ 
takable traces of glacial action upon all the 
islands along the coast of New England, some¬ 
times lying at a very considerable distance 
from the mainland, give an approximate, though 
a minimum, measure of the former extent of 
the glacial drift seaward, and the subsequent 
advance of the ocean upon the land. Like 
those of the harbor of Para, all these islands 
have the same geological structure as the con¬ 
tinent, and were evidently continuous with it 
at some former period. All the rocky islands 
along the coast of Maine and Massachusetts 
exhibit the glacial traces wherever their sur¬ 
faces are exposed by the washing away of the 
drift; and where the drift remains, its char¬ 
acter shows that it was once continuous from 
one island to another, and from all the islands 
to the mainland. 
It is difficult to determine with precision the 
ancient limit of the glacial drift, but I think it 
