Xo.i.] GRAY AND HOOKER ON THE ROCKY MOUNTAIN FLORA. 65 



Tin* narrow district oooapied by the I'a« iii. forest has ■ maofa mora aneqna] rainfall, 

 ■on aneqaal in its different part-.. most aneqnaJ in the different leaaom of I b< 

 \»ry different in the Bame place in different 



I'ii 'in the Golf of Mexico to the Golf of Bt. Lawrence the amonnt of rain deon 

 moderately and rather regularlj from sooth to oortfa ; hot, at less la Deeded in ■ eold 

 climate, there is enough to aonriah foreet throughout. <>n the Pacific coast, from tin- 

 Gulf of California to Paget Sound, the southerly third baa almost no rain at all ; the 

 middle portion lees than our Atlantic least ; the northern third has about our Atlantic 

 ge. 



Then, New England has about the same amount of rainfall in winter and in summer; 

 Florida and Alabama about one-half more in tin- three Bummer than in the t bree winter 

 months — a fairly equable distribution. Hut on the Pacific coast there is no summer 

 rain at ail, «x« «pr in the oorthern portion, and there little. And the winter rain, of 

 forty-four inches on the northern border, diminishes to less than on. -halt' before reach- 

 ing the Hay of San Francisco; dwindles to twelve, ten, and eight inches <»n the 

 southern coast, and to tour inches before we reach tin- United States boundary below 

 San 1>: _ 



Taking the whole year together, and confining ourselves to the roast, the average 

 rainfall for the year, from Puget Sound to the border of California, is from eighty 

 inches at the north to seventy at the south, i. e.. seventy on the northern edge of 

 California: thence it diminishes rapidly to thirty-six. twenty (about San Fran< 

 twelve, and at San Diego to eight inches. 



The two rainiest regions of the United States are The Pacific coast north of latitude 

 forty-five, and the northeastern coast and borders of the Gulf of Mexico. But when 

 one is rainy the other is comparatively rainless. For while this Pacific rainy region 

 ha- only from twelve to two inches of its rain in the summer months. Florida, out of 

 Ma forty to sixty, has twenty to twenty-six in summer, and only six to ten of it in the 

 winter months. 



Again, 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 aud 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 Pacific forest is so magnificent in its development. 



Equally, in the rapid decrease of rainfall southward, in its corresponding restric- 

 tion to one season, in the continuation of the Cascade mountains as the Sierra Nevada, 

 cutting off access of rain to the interior, in the unbroken stretch of coast ranges near 

 i. and the consequent small and precarious rainfall in the great interior valley 

 of California, we see reasons why the Californian forest is mainly attenuated south- 

 ward into two lines — into two files of a narrow but lordly procession, advancing 

 southward along the coast ranges, aud along the western flank of the Sierra Nevada, 

 :ig the long raUsy between comparatively bare of trees. 



By the limited and precarious rainfall of California, we may account for the limi- 

 tations of its forest. But how shall we aoOOUUl for the foot that this dist: 

 iratively little rain produces the Is - in the w. I only pro.: 



alone of all the world, those two pCCUlJ I - Which excite our special WOndSt — 



xtraordinary growth inijjht b 

 I - aid Fir- t rees, who-.- brethren w.- know, and ■ mate 



upon a scale only less gigantie. Evidently there is sot: 

 5 G B 



