The next subject relative to the Oregon country is its geological character. In remarking upon the geology of this country several departments of the science are presented to view. First, there are three ranges of mountains running nearly parallel with each other from north to south.
The eastern range which bounds the eastern side of Oregon, is along the dividing ridge of the American continent. If the question be asked, why this dividing ridge? the geologist alone attempts an answer. From the accumulation of facts hitherto adducd of the liquidity of the earth’s interior, and the discharge for ages of its internal liquid matter upon the already formd crust, it is evident that its nucleus must become less than at first, and thereby produce a rigid and furrowd appearance of the crust, by its conforming through the power of gravitation to a lesser surface than that on which it was at first formd. Altho’ isolated peaks of mountain ranges may be formd by accumulation of lava, and considerable districts may be raisd by the pressure of gasses from beneath, yet so considerable an elevation as the dividing ridge of the American continent can never be formd in such a way.
Oregon is truly an uneven and mountainous country. It is true that in passing from the dividing ridge westward, there are a few situations where the traveler views the country around him as apparently level, but this appearance continues on advancing along, but a short distance, till he is plunged into almost inextricable gulfs and deep ravines. The Blue mountains or intermediate range between the dividing ridge and the Cascade range, are of minor importance. They traverse no considerable extent of country, nor are they very wide. They have a volcanic appearance, and are strewd over with vescicular lava.
The Cascade range of mountains are more extensive, traversing by different names the whole of Oregon and California, at a distance of from 100 to 200 miles from the Pacific ocean. Some of its peaks are high and coverd with perpetual glaciers. This range, like the dividing ridge, seems to have been elevated by compression.
Between the Willamet valley and the ocean, is a range of high hills calld the Coast range. These are too rugged to admit of cultivation.
The western shore of Oregon is rocky, and in many places precipitous. If the theory that ocean beds are formd by undulations in the earth’s crust be true, the query might arise, Why are ocean limits of precipitous rocks of the firmest material, as is the case with many of the ocean shores, and not a gradual slope from the land downward to the bed of the ocean? If it be admitted that rivers are formd by the expansive force of gasses acting beneath the earth’s crust, it may be supposd that a fissure by similar means may be formd parallel and near to the shore of an ocean, so that its waters by their weight may produce a subsidence of that portion lying under them, whilst that part opposite the fissure remaind stationary.
Oregon may be regarded as a primary country. Few fossiliferous rocks are seen in any part of it. I noticd on the west bank of Big Sandy creek, about thirty miles west of South pass, a few fossiliferous shale rocks. I have not noticd any in other places, though they may exist sparingly. From the American falls on Snake river, for several hundred miles westward the country is overlaid with a stratum of basaltic lava. This seems to be the true basalt, and although the rocks of the Willamet river at Oregon city have been considerd by some as basalt, from their extreme hardness, yet I have noticd that the surface of those rocks, after having been exposd to the weather, become a mere sand rock, by the loss of the iron with which they are impregnated. It is well known to mineralogists, that iron becomes soluble by the action of the atmosphere upon it, by which means water carries it from its parent bed to lower levels, where it is deposited, under the name of bog ore. The rocks at Oregon city consist of about three varieties of rock, differing not essentially in their properties, though some of them appear to have been subjected to so high a degree of heat as to render them somewhat crystaline or vitreous. The rocks at Oregon city are so fully impregnated with iron, that the magnetic needle, at some points along these rocks, is drawn aside from its polar position.
From what information I have obtaind in addition to my own observation respecting the rocks of Oregon, I am satisfied that few rocks except those of a silicious formation, exist here. Along the Columbia river, near its mouth, are a few lime rocks of inferior quality. At the Cascade falls, are whole trees of silicious petrefaction, showing distinctly the grains of the timber, and to what kind they belongd.
As the Willamet river has hitherto attracted the attention of actual settlers more than any other tributary of the Columbia river, I have concluded to give a more particular description of it than any other one belonging to the Western division of Oregon. From its confluence with the Columbia to the high country of its sources, the Willamet traverses a distance of about two hundred miles in extent. Its union with the Columbia is not much short of one hundred miles from the ocean. At the mouth of the Willamet, is a delta fifteen or twenty miles in length, calld Souvie’s island, running nearly parallel with the Columbia. This island was formerly the residence of immense numbers of Indians. The Hudson Bay Company at present occupy it for farming purposes. At the eastern or upper mouth of the Willamet, are one or two other small deltas, though of no importance.
About fifteen miles from the Columbia, on the west bank of the Willamet, is a small town calld Portland. Ships of considerable burden visit this place for their lading.