ATLANTIC PL*AIN. 
211 
'leys very extensive. It embraces a variety of fine 
soils, and immense water-power in its rivers and 
running streams. The tract lying between this and 
the Atlantic is low and monotonous in its aspect, 
having an average width of from 100 to 150 miles, 
and an elevation of about 100 feet. This has been 
called the Atlantic Plain of the United States, and 
we shall so designate it. 
Professor Rogers remarks, that " the surface of 
this plain is everywhere scooped down from the 
general level to that of the tide by a multiplicity of 
valleys and ravines, the larger of which receive 
innumerable inlets and creeks, while the smaller 
contains marshes and alluvial meadows. The whole 
aspect of the barrier of primary rocks forming the 
western limits of this plain, forcibly suggests the 
idea that at a rather lower level they once formed 
the Atlantic shore, and that they exposed a long 
line of cliffs and hills of gneiss to the fury of the 
ocean ; a survey of the plain just described* as 
strongly suggests the idea that all of it has been 
lifted from beneath the waves by a submarine force, 
and its surface cut into the valleys and troughs it 
presents by the retreat of the upheaved waters." 
This tract embraces a large proportion of the newer 
secondary and tertiary formations hitherto investi- 
gated upon this continent, and we are better ac- 
quainted with its organic remains than almost any 
other region, not only from the extensive denuda- 
tion of its surface, but from the circumstance that 
its horizontal strata are admirably exposed in the 
deep cuttings and vertical banks of its rivers, often 
through many miles in extent. 
The great central basin of North America spreads 
from the Alleghanies to the Rocky Mountains, and 
from the Gulf of Mexico to Hudson's Bay. It is 
* Report on the Geology of North America, at the fourth 
meeting of the British Association for the Advancement of Sci- 
