394 Observations on the Physical Geography, fyc. 



yielded as rain, on encountering the colder airs and colder coun- 

 try reached in their progress north. 



The Westerly winds alluded to are well known to pertain to 

 the great circuits of the atmospheric currents. As the trades 

 (easterly winds) prevail over a large part of tropical latitudes, 

 below the parallel of 25° or 30°, so westerly winds prevail in 

 extratropical latitudes north and south of latitude 30° or 35°.* 

 These winds arc even more regular and constant in the Pacific 

 than in the Atlantic, — both north and south of the equator; and 

 vessels are accustomed to take advantage of them in their voyages 

 across the ocean. 



From the survey of facts which has been made, it is apparent 

 that the prevalence of oceanic westerly winds in connection with 

 the in frequency of northern land breezes, is the cause of the 

 mildness, as well as dryness of the climate of Northwestern 

 America. It has determined the distribution and limits of the 

 forest and prairie regions, and has originated the barren semi- 

 deserts of inner and lower California. The great Dividing 

 Mountains of the Territory (the Cascade Range and its Southern 

 continuation) prove a partial barrier to these ocean winds, pre- 

 venting them more or less from carrying their moisture easterly 

 and scattering too widely the scanty allowance to benefit essen- 

 tially the country; they gather the vapors partly in solid snows 

 about their heights, and partly in mists and rains, thence to 

 impart waters to streams that flow down and irrigate the wide 

 valleys. A region along the Pacific is thus cut off from the arid 

 interior and rendered fertile ; and its salubrity is farther enhanced 

 by the cool airs from the mountains poured at night upon the 

 heated plains. The long parallelism of the mountain ranges to 

 the coast, has given great length to the rivers by forcing the wa- 

 ters over a large area into a few main streams that make a long 

 and devious way to the sea, expanding thus the alluvial prairies 

 and distributing channels of internal navigation. By such means, 

 the Western section of the Territory is made to abound in agri- 

 cultural and pastoral resources, and is supplied with extensive 

 forests, while the region east of the Dividing Mountains is compar- 

 atively unproductive. The former may become densely populated 

 and full of activity iirall the varied pursuits of civilized life; the 

 latter promises a support only for widely scattered herdsmen, with 

 here and there a village or town where a large stream gives suf- 

 ficient water for irrigation. 



Mr. Wm. C. I 

 3sition of this 



whom we have already referred, has given us the best 

 lis memoirs. See this' Journal, xx, 50, 1831 ; xxv, 12*, 



1834; xxviii, 314, 1835; xxxiii, 61, 1838; xlv, 295, 302, 1843. 



I 



