Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/889

Rh shrubbery. All about these lower plains are well-marked terraces, composing the higher levels, and from these, cast, west, and south to the encircling mountains, are spread away the rolling fertile uplands, gradually merging into the dense fir and pine forests which crown the higher summits. Many things attest the former presence of an arm of the sea extending from Puget Sound to the southern end of the valley. Many basaltic ridges yet remain, but this rock has been largely washed away. Western Oregon is well supplied with the ordinary building stones, as granite, syenite, and sandstone. Marble and limestone are found in the extreme south-west, and a valuable cement stone in the valley of the Umpqua. The Umpqua is a rapid mountain stream, and its valley is narrow but extremely fertile. This and Rogue river break through the Coast range in cañons, deep, rugged, and heavily timbered. The valley of Rogue river is beautiful, with a delightful climate, but it has always been very difficult of access, and has only now been reached for the first time from the north by the railroad. Much gold has been taken from the placer mines of the valley, and the sands and gravels of nearly all the tributary valleys carry the precious metal. The country lying between the Coast range and the ocean is narrow and very rugged, with some small cultivable valleys very difficult of access. There are no good harbours on the coast, but the Government is making efforts to improve Coos and Yaquina bays and Port Orford.

The Columbia river enters the Pacific Ocean near the 46th degree of north latitude; it drains by means of its tributaries the western slope of the Rocky Mountains, from about the 42d to the 53d parallel, a distance of 900 miles. The area of its drainage-basin is nearly 245,000 square miles. The route of communication by the Columbia has been of the greatest importance in the early development of Oregon, and its value increases daily. The head of navigation for sea-going ships is at Portland, about 100 miles up the Columbia and 12 miles up the Willamette. From this point up to the Cascades, river craft go freely with plenty of water at all seasons of the year, with, generally, the exception of a short time each winter when the river is frozen. The cascades of the Columbia are due north from Mount Hood, just on the central line of the range where it is cut through by the river. The obstruction to navigation here is complete; but the Government has for several years been engaged in the construction of a canal which will make navigation continuous 45 miles farther, up to the Dalles, at the eastern base of the Cascades. Here there is another total obstruction, the river flowing swiftly through intricate channels, which seem to have been originally great cracks in a field of lava; surveys have been made, however, and plans prepared for improvements. Above the Dalles the Columbia is navigable for 190 miles and the Snake for 180. The Northern Pacific Railroad passes down on the Oregon side, through the cañon of the Columbia. The Columbia is noted for its beautiful scenery, for the great quantity of salmon taken from its waters, and for the dreaded bar at its mouth. The dangers from this bar have been greatly lessened of late years by improved pilotage and more accurate knowledge of the phenomena; and further ameliorations by the general Government are in contemplation.

The south-west warm winds from the Pacific distribute vapours over western Oregon abundantly in autumn, winter, and spring in dews, fogs, rains, and occasional snows, and over eastern Oregon in less amounts. The north-west summer winds are cool. The average temperature in western Oregon is &mdash; in spring 52º, in summer 67º, in autumn 53º, and in winter 39º Fahr. The thermometer

seldom rises above 90º in the hottest days of the summer, and rarely falls below 20º in the winter. In the thirteen years 1849-51 and 1858-68, two-thirds of the days were pleasant, and only one -third were either showery or rainy or snowy in the north-west part of the State. In the Willamette valley the average yearly rainfall is 44 to 54 inches, which is about the same as at Philadelphia and at Davenport (Iowa). In the Umpqua and Rogue river valleys it is somewhat less. Thunder-storms seldom occur in the State, and cyclones and tornadoes are unknown.

{{EB1911 Fine Print|Geology. &mdash; The geological history of the Cascade and Coast ranges of Oregon is very interesting. For an immense period before these ranges existed the primeval ocean washed the western shores of the great Rocky Mountain chain, and throughout the Paleozoic era and the whole Triassic and Jurassic periods of the Mesozoic era numerous rivers kept bringing down debris until an enormously thick mass of off-shore deposits had accumulated. This marginal sea-bottom became the scene of intense aqueo-igneous action in its deeply-buried strata, producing a line of weakness, which, yielding to the horizontal thrust produced by the secular contraction of the interior of the earth, was crushed together and swollen up into the Sierra Nevada and Cascade Mountains at the end of the Jurassic period. The range thus produced, as far as can be ascertained, was not of very great height, though probably higher to the south than to the north. It existed for unknown centuries, and in its turn was the theatre of erosion and plant-growth, and was roamed over by the now extinct fauna of the Cretaceous and Tertiary periods. It was not yet covered by the great lava-flow and mountain range of the modern Cascades, but by forests of conifers and oaks. Beneath the overlying lava, where the Columbia breaks through the range, there is found along the water's edge, and for about 15 feet upwards, a very coarse conglomerate of rounded porphyritic pebbles and boulders of all sizes up to 6 feet in diameter, held together by an imperfectly-lithified earthy paste. Above this conglomerate is a very distinct irregular old ground-surface bed, in which are found silicified stumps with roots extending over a diameter of 20 feet and penetrating into the boulder material beneath, evidently in situ. Resting directly on this forest ground-surface, and therefore enclosing the erect stumps, is a layer of stratified sandstone, 2 or 3 feet thick, filled with beautiful and perfect impressions of leaves of several kinds of forest trees, possibly of the very trees about whose silicified bases they are found; this layer is not continuous, like the ground-surface on which it rests. Above this leaf-bearing stratum rests a coarse conglomerate similar to that beneath at the water-level. Scattered about in the lower part of this upper conglomerate and in the stratified sandstone, and sometimes lying in the dirt-bed beneath it, fragments of silicified drift-wood are found. Above this last conglomerate, and resting upon it, rise the layers of lava, mostly columnar basalt, one above another, to a height of more than 3000 feet. The following order of events has been deduced from these facts by Professor Le Conte, their first observer.

The region of the Columbia river was a forest, probably a valley, overgrown by conifers and oaks. The subsoil was a coarse boulder drift produced by erosion of some older rocks. An excess of water came on, either by floods or changes of level, and the trees were killed, their leaves shed and buried in mud, and their trunks rotted to stumps. Then came on a tumultuous and rapid deposit of coarse drift, containing drift-wood, which covered up the forest ground and the still remaining stumps, to a depth of one, perhaps several, hundred feet. The surface thus formed was eroded into hills and dales, and then followed the outburst of lava in successive flows, and the silicification of the wood and cementation of the drift by the percolation of the hot alkaline waters containing silica. Finally followed the process of erosion by which the present stream, channels, and valleys, whether main or tributary, have been cut to their enormous depths. The great masses of sediment sent down to the sea by the erosion of the primary Cascade range, forming a thick off-shore deposit, gave rise in turn at the end of the Miocene to the upheaval of the Coast range, the Cascade Mountains being at the same time rent along the axis into enormous fissures, from which outpoured the grand lava-floods, building the mountains higher, and covering the country for great distances. This is probably the grandest lava-flow known to geology, covering as it does an area of about 200,000 square miles. Commencing in middle California as separate streams, in northern California it becomes a flood, completely mantling the smaller and flowing around the greater inequalities. In northern Oregon and Washington it becomes an absolutely universal flood, beneath which the whole original face of the country, with its hills and dales, mountains and valleys, lies buried several thousand feet. It covers the greater portion of northern California and north-western Nevada, nearly the whole of Oregon, Washington, and Idaho, and runs far into British Columbia on the north. The average thickness is <!--