Origin of the rich soil of East Washington.Whether the extremely fertile soil which overlies the basalt in East Washington is a top-dressing of volcanic ashes, or is decomposed basalt, cannot readily be determined. It cannot be referred to the Glacial period, as I observed no appearance of drift anywhere except in the valley of Spokane River. Such a wide spread of lava is not unexampled in view of somewhat similar overflows now occurring at intervals in the Sandwich Islands, where lava runs and spreads itself like water. These Hawaiian flows are mentioned by Captain C. F. Dutton in his report of the Zuni Plateau.
A ledge of sandstone belonging to the Meiocene Tertiary is visible under the basalt at the lower cascade in the Columbia River; and a stratum of iron ore and vegetable matter is found on the Willamette at Oswego, lying horizontally between great masses of basalt, showing a long interval between overflows. The volcanoes not wholly extinct.These eruptions probably continued with diminishing force until near the present time. It is reported that Mount Hood has sent out smoke or steam since the settlement of Oregon. The crater of Mount Ranier was visited by two gentlemen within a few years, and a night spent in its bottom by the side of a jet of steam. Such, at least, is the account given by one of them, Mr. Stevens.
Glacial drift.The Quaternary or Drift Period has left abundant, though by no means universal, traces of its presence. As before intimated, I saw no relics of it in East Washington, except a deposit of rather small, generally very small, and well-rounded quartz gravel, thickly strewing, and really forming, the flats bordering Spokane River. This gravel macadamizes the streets of the City of Spokane Falls, and the neighboring roads, so as to make them firm at all seasons. These gravelly bottoms are not tillable except in a few spots.
The undulating country north and east of Puget Sound is in many places deeply covered with drift material which shows the effect of both ice and water. Blocks of partially rounded granite several feet in diameter are found on the hills around Seattle. This gravel deposit is not often found on high points, but there is a ridge in the Cascade Mountains, near Salal Prairie, which is thickly bestrewed at an elevation of 1,000 feet. This, however, was quite exceptional, and may be the lateral moraine of a local glacier. The deposit around Seattle is not only easy to cultivate (its soil being a light blue loam), but seems fertile. The bottom lands are free from gravel.
So much for the general geology.
ECONOMIC GEOLOGY.
Note.—The location of the coal-fields and collieries mentioned in the following pages may be seen on an accompanying map.
Under the head of Economic Geology, I shall describe with more detail the mineral beds which have a commercial value, and in the following order:—I. Coal; II. Iron Ore; III. Granite, Limestone, and Marble; IV. Precious and Base Metals.Thickness of the Coal Measures.
I. Coal.—The thickness of the Coal Measures of the Puget Sound basin is estimated by Bailey Willis at something like 14,000 feet, though he admits the obvious possibility of error in the calculation by reason of undiscovered faults. We may fairly expect them, however, to be thicker than the same group in the Rocky Mountains, which measure about 9,000 feet. As heretofore remarked, the sediments become thinner from west to east. Of course, the maximum thickness is not to be expected in every locality. Mr. Willis's estimate was made in the Wilkeson and Green River fields, and really did not reach the limit of the coal-bearing rocks. The coal rocks of the Cedar River and Snoqualmie basin have never, so far as I know, been estimated, but probably this group is equal in thickness to that of any other part of the field. The difficulty of measurement arises from the numerous fractures and changes of strike which exist.
Fifteen workable seams.The number of distinct workable seams of coal of three feet and upwards, belonging to the measures, may safely be put down at not less than fifteen.