438 A JOURNEY IN BRAZIL. 



seeking their natural level, gradually widening and deep- 

 ening the channels in which they flowed, as they worked 

 their way down to the sea. When they reached the shore, 

 there followed that antagonism between the rush of the 

 rivers and the action of the tides, between continental 

 outflows and oceanic encroachments, which still goes on, 

 and has led to the formation of our Eastern rivers, with 

 their wide, open estuaries, such as the James, the Potomac, 

 and the Delaware. All these estuaries are embanked by 

 drift, as are also, in their lower course, the rivers con- 

 nected with them. Where the country was low and flat, 

 and the drift extended far into the ocean, the encroach- 

 ment of the sea gave rise, not only to our large estuaries, 

 but 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 unmistakable traces of glacial action upon 

 all the islands along the coast of New England, sometimes 

 lying at a very considerable distance from the main-land, 

 give an approximate, though a minimum, measure of the 

 former extent of the glacial drift seaward, and the sub- 

 sequent advance of the ocean upon the land. Like those 

 of the harbor of Para, all these islands have the same 

 geological structure as the continent, and were evidently 

 continuous with it at some former period. All the rocky isl- 

 ands along the coast of Maine and Massachusetts exhibit 

 the glacial traces wherever their surfaces are exposed by the 

 washing away of the drift ; and where the drift remains, 

 its character shows that it was once continuous from one 

 island to another, and from all the islands to the main-land. 

 It is difficult to determine with precision the ancient 

 limit of the glacial drift, but I think it can be shown 



