CLIMATIC FACTORS 113 



of the rain-bearing winds. The windy side catches the precipitation; 

 on the other side there is a minimum of rainfall. The Limagne in the 

 shadow of the Mont Dore of Auvergne, the low plains of the upper 

 Rhine east of the Vosges, the eastern slopes of the Scandinavian 

 mountain plateau are relatively dry spots in "rain shadows." The 

 peculiar xeric vegetation of the deep inner valleys of the Alps repre- 

 sents a minimum of rainfall between two pronounced maxima. 



Anyone who has traveled across the Alps between Berne and Domo 

 d'Ossola, or between Bolzano and Bregenz, will certainly remember the 

 sudden change of vegetation on entering and on leaving the great 

 longitudinal valleys of the Central Alps. In the humid outer ranges, 

 on both sides, beech wood and mixed deciduous forests with abundant 



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Jan. Feb. Mar April May June Ju/y fiu^. Sept. Oct A'ov. Dec 



Fig. 62. — Periodicity of the Mediterranean, Atlantic, and Central European rain 



climates. 



epiphytic lichens and mosses grow luxuriantly in the resulting moisture 

 from the two maxima of rainfall. Within the valleys (Valais, Vinsch- 

 gau, Unterengadine) are pine forests, juniper bushes, and sunburned 

 dry grassland, overarched by the azure rainless skies of the Central 

 Alps. 



Quite astounding is the sudden transition from the belt of cedars 

 and oaks on the rainy western slopes of the middle Atlas (with 70 to 80 

 cm. of precipitation) into the blazing, scorching desert steppe of the 

 upper Moulouya (annual rainfall about 20 cm.). Within a few hours 

 the traveler may traverse two worlds. Still more violent contrasts 

 in climatic moisture are met in the Himalayas. But altitude also 

 figures there, and the distances are on a gigantic scale. 



Perhaps nowhere in the world is the influence of mountain ranges on 

 rainfall more strikingly shown than in western North America. The 

 Cascade Mountains intersect the states of Washington and Oregon 



