6Q BULLETIN UNITED STATES GEOLOGICAL SURVEY. [FoJ.VI. 



able to the development of trees, especially of coniferous trees ; and it is not easy 

 to de ermine what it can he. 



Nor, indeed, does the rainfall of the coast of Oregon, great as it is, fully account 

 for the extraordinary development of its forest; for the rain is nearly all in the 

 winter, very little in the summer. Yet liere is more timber to the acre than in any 

 other part of North America, or perhaps in any other part of the world. The trees 

 are never so enormous in girth as some of the Californian, but are of equal height — 

 at least on the average — three hundred feet being common, and they stand almost 

 within arms' length of each other. 



The explanation of all this may mainly be found in the great climatic differences 

 between the Pacific and the Atlantic sides of the continent ; and the explanation of 

 these differences is found in the difference in the winds and the great ocean currents. 



The winds are from the ocean to the land all the year round, from northwesterly iu 

 summer, southwesterly in winter. And the great Pacific Gulf Stream sweeps toward 

 and along the coast, instead of bearing away from it, as on our Atlantic side. 



The winters are mild and short, and are to a great extent a season of growth, 

 instead of suspension of growth as with us. So there is a far longer season available 

 to tree-vegetation than with us, during all of which trees may either grow or accu- 

 mulate the materials for growth. On our side of the continent and in this latitude, 

 trees use the whole autumn in getting ready for a six-months winter, which is com- 

 pletely lost time. 



Finally, as concerns the west coast, the lack of summer rain is made up by the 

 moisture-laden ocean winds, which regularly every summer afternoon wrap the coaat 

 ranges of mountains, which these forests affect, with mist and fog. The Redwood, 

 one of the two California Big-trees — the handsomest and far the most abundant and 

 useful — is restricted to these coast-ranges, bathed with soft showers fresh fyom the 

 ocean all winter, and with fogs and moist ocean air all summer. It is nowhere found 

 beyond the reach of these fogs. South of Monterey, where this summer condensation 

 lessens, and winter rains become precarious, the Redwoods disappear, and the gen- 

 eral forest becomes restricted to favorable stations on mountain sides and summits. 

 * * * The whole coast is bordered by a line of mountains, which condense the 

 moisture of the sea-breezes upon their cool slopes and, summits. These winds, con- 

 tinuing eastward, descend dry into the valleys, and, warming as they descend, take 

 up moisture instead of dropping any. These valleys, when broad, are sparsely 

 wooded or woodless, except at the north, where summer rain is not very rare. 



Beyond stretches the Sierra Nevada, all rainless in summer, except local hail-storms 

 and snowfalls on its higher crests and peaks. Yet its flanks are forest-clad; and, be- 

 tween the levels of 3,000 and 9,000 feet, they bear an ample growth of the largest Co- 

 niferous trees known. In favored spots of this forest — and only thei'e — are found those 

 groves of the giant Sequoia, near kin of the Redwood of the coast-ranges, whose trunks 

 are from fifty to ninety feet in circumference, and height from two hundred to three 

 hundred and twenty-five feet. And in reaching these wondrous trees you ride through 

 miles of Sugar Pines, Yellow Pines, Spruces, and Firs, of such magnificence in girth and 

 height, that the Big-trees, when reached — astonishing as they are — seem not out of 

 keeping with their surroundings. 



I cannot pretend to account for the extreme magnificence of this Sierra Forest. Its 

 rainfall is in winter, and of unknown but large amount. Doubtless most of it is in 

 suow, of which fifty or sixty feet falls in some winters ; and — different from the coast 

 and in Oregon, where it falls as rain, and at a temperature which does not suspend 

 vegetable action — here the winter must be complete cessation. But with such great 

 snowfall the supply of moisture to the soil should be abundant and lasting. 



Then the Sierra — much loftier than the coast-ranges — rising from 7,000 or 8,000 to 

 11,000 and 14,000 feet, is refreshed in summer by the winds from the Pacific, from 

 which it takes the last drops of available moisture; and mountains of such altitude, 

 to which moisture from whatever source or direction must necessarily be attracted, 



