White shales

Gerelateerde afbeelding

There are white shales as well, and waterlaid strata of white volcanic ash. As these sediments thicken to a depth approaching six thousand feet, the lake that rests upon them is always shallow, and full of freshwater clams and snails, and some beavers and aquatic mice. While the lake is accepting sediment, the bottom of its bottom is sinking at the same rate. With a loud terminal hissing, lavas flowing down from Yellowstone cool in the lake as obsidian. Fiery billows of sticky fog come down the valley as well. It cools as tuff. The big lake vanishes. In successive earthquakes, there is more valley faulting, damming the valley streams to form deep narrow zakelijke energie vergelijken lakes, which appear suddenly and as quickly go. Off the fast-rising block of mountains, erosion has by now removed fifteen thousand feet of layered sediments, and the Precambrian granites-with their attendant amphibolites, schists, and gneisses, and a vertical streak of diabase-are the highest rock below the sky. Bent upward against the flanks of the Precambrian are the brokenoff strata of the Paleozoic era, and the broken-off strata of the Mesozoic era-serrated, ragged hogbacks, continually pushed aside. Perched on the granite at the skyline is a bit of Cambrian sandstone that the weather has yet to take away. On the opposite side of the Teton Fault, the same sandstone lies beneath the valley. The vertical distance between the two sides of this once contiguous formation is thirty thousand feet. That brings the chronicle essentially to the present, but still the blackish mountains look more like hips than breasts. Now off the Absarokas, off the Wind Rivers, off the central Yellowstone Plateau-and, to a lesser extent, down the canyons of the Tetonscomes a thousand cubic miles of ice. A coalesced zakelijke energie glacier more than half a mile thick enters and plows the valley. The west side of this glacier scrapes along the Tetons above the level of the modern timberline. Melting away, the glacier leaves a barren ground of boulders. More ice comes-a lesser but not insignificant volume-and a third episode, which is smaller still.