14 PHYSIOGRAPHY 



frequently been the boundaries of political states. The mountains 

 of western and southwestern Europe were one cause of the numerous 

 small political divisions of those regions. Mountainous highlands 

 have repeatedly given refuge to weak peoples, driven by their 

 stronger enemies from the more desirable lowlands. The almost 

 inaccessible mountain strongholds of Scotland, Wales, and parts of 

 India enabled such peoples to maintain their independence for long 

 periods. The Appalachian Mountains kept the English settlers 

 on the eastern border of North America for nearly a century and a 

 half, and influenced their life in many ways. Later, grave political 

 dangers arose from the fact that the seaboard was separated from 

 the valley of the Ohio by the same system of mountains. 



SUBORDINATE TOPOGRAPHIC FEATURES 



The surfaces of most plains and plateaus are uneven, while the 

 very name of mountain suggests ruggedness. Irregularities of 

 surface consist of elevations, such as ridges and hills, above the 

 general level, and of depressions, such as valleys and basins (depres- 

 sions without outlets) below it. The elevations and the depres- 

 sions are bordered by slopes, which, when steep, are called cliffs. 

 Ridges, hills, valleys, basins, flats, cliffs, etc., affect mountains, 

 plateaus, and plains; but they are usually more pronounced in 

 mountains and plateaus than on plains. These minor unevennesses 

 of surface are topographic features of the third order, and will be the 

 subject of future study. The key to their history is found in the 

 changes now taking place on the land, or in those which have taken 

 place in recent times. 



CHANGES Now TAKING PLACE ON THE LAND 



Certain familiar changes are always taking place on the land. 

 Some of them are brought about by the atmosphere, some by water, 

 some by ice, some by the life of the earth, and some in other ways. 



1. The air is nearly always in motion, and whenever it blows 

 over a surface on which there is dust, some of the dust is picked up 

 and carried to some other place. Grains of sand are blown about 



