"The sound of streams that swift and slow, Draw down Æonian hills, and sow The dust of continents to be." This slow disintegration of the earth's first land continued for millions of years, the waste accumulating along the shores, and as far out as the finer sediment could be carried. Finally the pressure on the edges of this land caused the thin crust to soften and break, the molten magma poured forth in great masses, and the thick sediments were smashed together, folded up and thrust upward to form the earth's _first hills_. [Figure 156: A PORTION OF THE COLUMBIAN LAVA FLOW IN THE STATE OF WASHINGTON. Photograph by Asahel Curtis, Seattle.] The crust was then so thin and easily broken that only low hills appeared but after it became thicker it was not so easily rent and _mountain ranges_ were born with an accompanying roar of tremendous volcanoes. Geologists, studying the ages of the different ranges in the United States, have concluded that the first to appear were the Appalachian mountains; later the Rocky mountains in the west, and still later the Coast ranges. Mountain ranges are invariably found along lines of very thick sediments. The same strata which along the Appalachian range are 40,000 feet thick, thin out, when traced westward, to only 4000 feet at the Mississippi River.[1] The high tablelands in portions of Idaho, Oregon and Washington were formed by great streams of lava which poured through many of the fissures of the coast ranges and buried the whole country above the hill tops. This lava cooled into thick massive layers of solid rock--an interesting sight to this very day. Although mountain ranges appear amid violence and their growth, in a geologic sense, is rapid, _plains_ and _plateaus_ are illustrations of sea-bottoms which have been covered with sediment carried down from the mountains,--mainly pebbles, sand and clay,--pressed and cemented together under the water and then gently raised to the surface. Sometimes the sea-bottom is exposed as a vast plain; again the strata are upheaved, bent or broken, forming faults and ridges. Many of the elevated plains and plateaus are later sculptured into hills by rains, winds, frosts and rivers. The hills are then gently torn down, the valleys filled up and the sediment again deposited by the rivers upon the bed of the ocean. "For every valley shall be exalted and every mountain shall be laid low." A few million years passed by and these same deposits may again be raised and become dry land. _The great stretches of land between the mountains of the eastern and western portion of America_ were formed from the sediment washed down from these mountains and deposited in the sea which lay between. The crust of the earth is still rising and sinking, the land gaining on the water, but as this is usually such a slow movement, it can only be traced through a period of many years.