ATLANTIC PttAIN. 



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- 

 ence. 



