324 PHYSICAL GEOGEAPHY. 



proceed to the inequalities of the form of the surface of 

 our planet, we have to consider mountains, either in re- 

 ference to their influence on the climate of neighbouring 

 lowlands, or to the climatic effects of their hypsometric re- 

 lations on their own summits, which often spread out into 

 elevated plains. Mountain chains divide the surface of the 

 earth into different basins, which are sometimes narrow and, 

 as it were, walled in, forming circular vail eys or calderas, which 

 (as in Greece and in parts of Asia Minor) occasion climates 

 locally individualised in respect to .warmth, humidity, 

 atmospheric transparency, and frequency of winds and 

 tempests. These circumstances have at all times exer- 

 cised a powerful influence on natural products, and on 

 cultivation; as well as on manners, institutions, and the 

 feelings with which neighbouring tribes mutually regard each 

 other. The character of geographical individuality, if we 

 may be permitted to use the expression, reaches its maximum 

 in countries where the variety of the form of the ground io 

 the greatest possible, both in the vertical and the horizontal 

 direction, both in relief and in the configuration of the coast 

 line. The greatest contrasts to this variety of ground are 

 found in the steppes of Northern Asia, in the grassy plains 

 (savannahs, llanos, and pampas)- of the new continent, in the 

 heaths of Europe, and in the sandy and stony deserts of Africa. 

 The law of the decrement of heat with increasing eleva- 

 tion in different latitudes has a most important bearing on 

 meteorological processes, on the geography of plants, on the 

 theory of terrestrial refraction, and on the different hypo- 

 theses on which the height of our atmosphere is estimated. 

 In the many mountain journeys which I have undertaken, 

 both within and beyond the limits of the tropics, the invest!- 



