FOREST GEOGRAPHY AND ARCHAEOLOGY. 209 



coast there is no summer rain at all, except in the northern 

 portion, and there little. And the winter rain, of forty-four 

 inches on the northern border, diminishes to less than one 

 hatf before reaching- the Bay of San -I&anciseo ; dwindles to 

 twelve, ten, and eight inches on tin- *thei-i roust, and to 

 four inches before we reach the I into ' Stotes boundary lie- 

 low San Diego. m 



Taking the whole year together, and confining < un- 

 to the coast, the average rainfall for the I'uget 

 Sound to the border of California, is from 

 the north to seventy at the south, /. /■., seven*? on ii. 

 northern edge of California ; thence it diminishes rapid 

 thirty-six, twenty (about San Francisco), twelve, and ai 

 Diego to eight inches. 



The two rainiest regions of the United States are th< 

 cific coast north of latitude forty-five, and the northen* 

 coast and borders of the Gulf of Mexico. Jnit when one is 

 rainy the other is comparatively rainless. For while this Pa- 

 cific rainy region has only from twelve to two inches of its 

 rain in the summer months, Florida, out of its forty to sixtv, 

 has twenty to twenty-six in summer, and only six to ten in the 

 winter months. 



A«*ain, the diminution of rainfall, as we proceed inland 

 from the Atlantic and Gulf shores, is gradual ; the expanse 

 that is or was forest-clad is very broad, and we wonder only 

 that it did not extend farther west than it does. 



On the other side of the continent, at the north, the district 

 so favored with winter rain is but a narrow strip, between the 

 ocean and the Cascade Mountains. East of the latter, the 

 amount abruptly declines, — for the year, from eighty inches 

 to sixteen ; for the winter months, from forty-four and forty 

 to eight and four inches; for the summer months, from 

 twelve and four to two and one. 



So we can understand why the Cascade Mountains abruptly 

 separate dense and tall forest on the west from treelessness 

 on the east. We may conjecture, also, why this north Pa- 

 cific forest is so magnificent in its development. 



Equally, in the rapid decrease of rainfall southward, in i' 



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