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 cations of the 
far West, the Mauvaises Terres, the summits of the Roeky 
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. 
