224 
PHYSICAL HISTORY OF THE 
masses, without any sign of stratification; 
. such differences in the formation being deter¬ 
mined by the state of the water, whether per¬ 
fectly stagnant or more or less agitated. Of 
such pool deposits overlying the drift there are 
many instances in the Northern United States. 
By the overflowing of some of these lakes, and 
by the emptying of the higher ones into those 
on a lower level, channels would gradually be 
formed between the depressions. So began to 
be marked out our independent river systems, 
—the waters always seeking their natural level, 
gradually widening and deepening 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 
