[Sidenote: The great sheets of basalt.] This great pile of basalt was built up by a succession of overflows of lava, the joints of which are plainly visible. The basaltic area, though perhaps thickest here, continues with a thickness of 1,000 to 1,500 feet up the Columbia for hundreds of miles; indeed the whole plateau, or prairie country of East Washington, which is a quadrilateral of some 200 miles in diameter, is but a continuation of the great lava-sheet seen at the Cascades and the Dalles. Through it the Columbia and Snake rivers have cut deep channels; and other, though shallower channels, have been cut across the surface of the plateau by departed streams. [Sidenote: 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. [Sidenote: 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. [Sidenote: 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.