Part 8 (2/2)
[Ill.u.s.tration: BRIDGE OVER THE SPOKANE RIVER, SEATTLE, LAKE Sh.o.r.e AND EASTERN RAILWAY.]
THE GEOLOGY OF WAs.h.i.+NGTON TERRITORY.
HISTORICAL AND STRUCTURAL.
I shall not say much about the historical geology of Was.h.i.+ngton Territory, because it contains some problems which have never been adequately studied, and which I had no opportunity to investigate. It is to be hoped that the regular work of the Government Survey may soon be extended to this important region. Hitherto it has been neglected. A few able geologists such as Joseph Le Conte, Pumpelly, Newberry, Bailey Willis, and some others, have made visits to the country on special errands; but except the treatise of Bailey Willis in Vol. XV. of the Census Reports, and some brief allusions to the country in systematic works on general geology, I had nothing to guide me as to the structure of the country, or the age of its deposits. For all practical purposes, however, I had no difficulty in understanding the work I had to do.
[Sidenote: The Western Coast regions younger than the Rocky Mountains and Appalachians.]
[Sidenote: An outlying Continent.]
[Sidenote: The rise of the West Coast.]
All agree that the country west of the Rocky Mountains proper, and including nearly all of California, Oregon, and Was.h.i.+ngton Territory, is geologically younger than the main range, and younger than the Appalachian country. At the close of the carboniferous period proper, the Rocky Mountain range const.i.tuted a separate continent, with a sea covering what is now the main Mississippi Valley, including the wide plains immediately east of the Rocky Mountains, and connecting, probably, with the polar sea, whilst the Pacific Ocean washed the western edge of this Rocky Mountain continent; so that until after that period there were no Wahsatch and Uintah mountains, no Sierra Nevada and Cascade Range, no Coast Range, and, of course, none of the intervening country. It is quite possible, however, that there was a third continent lying west of the present continent in what is now ocean, from whose waste the sediments were derived which were afterwards elevated and became the land now included in the three States bordering the Pacific, whilst the mother continent, which furnished the sediments, sank beneath the ocean. If there were such an outlying continent, additional force is given to the views of Dr. George F. Becker, endorsed by Dr. C. A. White, and to some extent antic.i.p.ated by Prof. J. D. Whitney, which render it probable on other grounds that the two great lines of mountains, viz., the Sierra Nevada and Cascade Range and the Coast Range, began their upward movement simultaneously during the early ages of the Juro-Trias.
The rise of these mountain lines was gradual and marked by reverse movements, whereby, after appearing above the surface, they sank and rose alternately, receiving fresh sediments, which, especially in the Was.h.i.+ngton Territory region and part of Oregon and California, when above water, became clothed with an enormous vegetation which was packed into coal-beds, layer after layer. In the lapse of time these all came above the surface. The mountains grew higher and higher, attended by intense heat in the axes of the ranges, and at different periods, down almost to the present, exhibiting volcanic action on an enormous scale.
At other periods, a large portion of the region was visited by ice-floods, succeeded by water-floods, which top-dressed great areas with a mingled deposit of gravel, sand and mud, and carried away vast blocks of the rocky substance of the country, and cut deep channels in all the highlands.
As Was.h.i.+ngton Territory is now presented to us, it exhibits a scene of mountains, lowlands, and elevated plateaus, which are full of interest and variety. Some general account of its topography has already been given.
[Ill.u.s.tration: LOWER SNOQUALMIE FALLS, 268 FEET HIGH, ON LINE OF SEATTLE, LAKE Sh.o.r.e AND EASTERN RAILWAY.]
[Sidenote: The rocks and minerals of the Cascade Mountains.]
The core of these high ranges is chiefly rock originally stratified, which has been metamorphosed by heat, and perhaps inside of all, with branches bursting out at various places, are plutonic rocks which have never been stratified. This is the state of things on the top of the Cascade Range, near Snoqualmie Pa.s.s, as well as on some subordinate peaks and ranges. On Mount Logan, the Denny Mountain, etc., are large bodies of syenitic granite whose age I have no means of determining.
a.s.sociated with this are quartzites of fine grain, and extremely hard, porphyries, and serpentinoid and chloritic rocks of different sorts, in which are imbedded the magnetic iron ores; and also large beds of crystalline limestone, both fine and coa.r.s.e grained. Crossing these, at various angles, are veins containing the precious and base metals.
[Sidenote: The metamorphic rocks of doubtful origin.]
Whether these rocks are Palaeozoic or Archaean in their origin, or whether they are simply the metamorphosed strata of the upper Juro-Trias, or the lower Cretaceous, is a question for future study. These plutonic and metamorphic rocks are believed to extend through the mountainous region lying north of the Columbia River; and they are reported also in the Coeur d'Alene Mountains. It is quite certain that on both flanks of the Cascade Mountains we find in their natural state Cretaceous conglomerates, sandstones, and shales bearing coal, at least in their upper beds. The deposits on the east side of the mountain have been much grooved and denuded, until we find only small areas of the Cretaceous strata on the Yakima and the Wenatchie rivers, and the Peshastan ridge between, with a patch of the coal-bearing rocks on the Yakima, and another on the Wenatchie. On the west side of the mountain range, the Cretaceous and coal-bearing areas are much larger.
[Sidenote: The coal beds.]
The coal deposits of all the Cretaceous regions of the West are regarded as belonging to the Laramie period which closed the Cretaceous age, and const.i.tutes a transition period between the Cretaceous and Tertiary. But I do not regard this question as settled. The inferior lignites of the Rocky Mountains, and the semi-lignites which const.i.tute the upper beds of the Was.h.i.+ngton Cretaceous coal properly belong to the Laramie period; but to include the underlying bituminous coals in the same group may be a matter of question. More will be said in reference to these coal beds under the next head. The Western coal-bearing rocks begin on outlying mountains, standing at the west foot of the main Cascade Range. These outlyers are irregular in size, height and direction; but many of them are 1,000 to 1,500 feet in height, and they are found in groups, separated by denuded s.p.a.ces, from the Cascade Mountains to the Pacific Ocean, and from the Canada line nearly to the Columbia River. The largest and most important field, however, lies south of the Snoqualmie River and between Puget Sound and the Cascade Mountains. Some of the coals found in the most southern part of the field, and on the Coast Range, are referred to the Tertiary period.
A smaller and wholly undeveloped field lies on the Skagit River, and another on, and west of Bellingham Bay. Similar beds are found on Vancouver's Island. Coal-bearing strata are found also on the Chehalis, Des Chutes, Nisqually and Cowlitz rivers. Whilst some of these southern and western strata are referred to the Tertiary period, there has been no systematic study of their geologic relations.
[Sidenote: The volcanic mountains and their great activity.]
It seems to be settled, however, that the lofty volcanic mountains which form conspicuous features in the scenery of the Cascade Range, were active in the Tertiary period, and not only built their own crests 9,000 to 15,000 feet high, but inundated much of the surrounding country with lava to an amazing breadth and depth. In this region, Mount Baker, Mount Ranier (also called Mount Tacoma), Mount St. Helens and Mount Adams in Was.h.i.+ngton Territory, and Mount Hood in Oregon, were the centres of the grandest operations; and so continued for ages.
[Sidenote: The wonderful canon of the Columbia River.]
We see gigantic results of this activity in the canon 1,000 to over 3,000 feet deep, which the Columbia River has cut through this volcanic matter in its pa.s.sage through the Cascade Mountains. This volcanic deposit consists of brown basalt, which in cooling crystallized into vertical, polygonal prisms, or columns, which have been sculptured by the weather into endlessly varied forms, beautiful, fantastic, and grand; altogether presenting a scene, or succession of scenes, for twenty-five miles, such as can nowhere else be equaled on the American continent, unless it be near by, on a tributary of the Columbia, the Des Chutes River of Oregon.
[Sidenote: The great sheets of basalt.]
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