GG BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Vol.Vi. 



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

 to <lc .inline wh.it it can he. 



Nor, indeed, dees 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. \ery little in the summer. Yet here is more timher 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 a~s some of the Californian, hut are of equal height — 

 ,it least on the average — three hundred feet heing common, and they stand almost 

 within arms' length of each other. 



The explanation of all this may mainly he 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 in 

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

 and along the coast, instead of hearing 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 coast 

 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 from 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 hordered 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 iu 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 there — are found those 

 groves of the giant Sn/uoia, 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 

 hnndredand t went y-iive t'rvt. And in reaching these wondrous trees you ride through 

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

 height, that the Big-trees, when reached — astonishing as they an — 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 luit large amount. Douhtless most of it is in 

 gnow, Of which fifty or M\t\ feet f;ills in some winters ; and — different from the coast 



and in Oregon, whew i1 Calls as rain, and ate temperature which does not suspend 



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

 snow tall the supply of moist me to the soil should be ahnndant and lasting. 



Then the Sierra — much loftier than the oeaettrsnges — rising from 7,000 or 8,000 to 

 11,000 and 14,000 feet, La refreshed in lumaserby the winds from the Pacifio, 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, 



