Page:An Illustrated History of the State of Oregon.djvu/22

 again. Animal life found food and drink and shelter, and still the changes went on. Frost and snow and raindrop and stormy winds and burning suns wrought the miracle of a new genesis, leaving a field in which Nature has written the most legible and astonishing records of her processes and her powers.

Proceeding eastward from the points indicated in the preceding paragraph, the Blue mountain range presents a wonderful conglomeration of basalts, granite, slate, sandstone, with vast beds of stratified sand and water-worn gravel. In places one formation predominates, in other places some other formation, and then again several of them appear intermixed, or overlying one another. It is evident that the heat attending the volcanic action that lifted this vast ridge to its present position was great enough to cause perfect fusion in only a few places; while yet the forces below were mighty enough to cause the wonderful and weird dis- placements of the primitive rocks so often arresting the observant eye in this wonderful range. One hour the traveler among these mountains will be passing over scoriated basalt, or along cliffs of basaltic columns, the next among great granite boulders or over gray granite pinnacles, then over miles of aqueous deposits in the form of stratified sandstone or stratified beds of sand and gravel intermixed; or again slate slopes and hillsides will arrest his eye, until he is lost in the wilderment of his strange surroundings.

The Blue mountains margin on the west the great lava plains of Snake river valley. Only a small part of that valley is in the State of Oregon, and it is hardly necessary to extend observations in regard to it. It may simply be stated that the volcanic conditions, so plainly marked in the Cascade and Blue mountains, and the valley intervening between them, continue and are intensified as we enter the great upper valley of Snake river, which lies mostly in the State of Idaho, which was once the mightiest scene of volcanic action on the American continent, if not in the world. As a few miles only of this vast lava plain fall within the limits of the State of Oregon, we can dismiss its marvels with these few general statements.

Perhaps, however, we should not dismiss the whole subject of the geology of this most interesting region, with these general statements for the lay render, without some more distinctly scientific [sic]d for the benefit of the more technical [sic]er and student. For him geology would [sic] about the following history of the conditions and changes of untold ages and marvelous processes through which this wonderful Oregon world was being formed.

For an immense period before the existence of the Coast and Cascade Ranges of mountains, the primeval ocean washed the western shores of the great Rock mountain chain, and throughout the palaeozoic 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 aqueous-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 upward into the Cascade and Sierra Nevada range at the close of the Jurassic period. The range thus produced was not of very great height. It existed for an- known centuries; the scene of erosion and plant-growth, roamed over by the now extinct fauna of the Cretaceous and Tertiary periods. It was combed by forests of conifers and oaks. Then followed the great lava-flow and uplift of the mountain range of the modern Cascades. Beneath the overlying lava, where the Columbia breaks through the barriers of this great range, there is found along the waters edge, and for nearly twenty feet upward, a course conglomerate of rounded porphyritic pebbles and boulders of all sizes up to six feet in diameter, held together by an imperfectly lithified earthly paste. Above the conglomerate is a very distinct, though irregular ground surface bed, in