TOPOGRAPHY OF THE EASTERN COAST. 



103 



landscape of the districts we have described, we cannot fail to 

 observe how strikingly it differs from terrestrial landscapes. 

 They present no proper parallel to the immense stretches of 

 hundreds of miles of gently sloping surfaces, such as form the 

 deepest part of the basin of the Gulf of Mexico, and of the 

 Eastern Caribbean, and the similar expanse of bottom which 

 extends along the whole Atlantic coast of the United States. 

 Aerial denudation is so powerful a factor that the least differ- 

 ence in the hardness of the material of adjoining tracts is 



Fig. 60. —Gulf of Maine. 



sufficient to effect very striking changes in level. These find 

 their ultimate expression, in connection with the geological 

 structure, in such characteristic regions as the canons of the 

 far West, the Mauvaises Terres, the summits of the Rocky 

 Mountains and of the Sierra Nevada, the Appalachian sys- 

 tem, the prairies of the West and the system of the Great 

 Lakes, the hydrographic basins of the Mississippi and of the 

 St. Lawrence. 



