The ash-consisting of very small shards of glass-had travelled about two hundred miles downwind from its volcanic source. Two hundred miles downwind from Mt. St. Helens, in the state of Washington, the amount of ash that has accumulated as a result of Mt. St. Helens’ recent eruptions is three inches. The ash here at the Continental Divide was sixty feet thick. A hundred and more miles northwest are remnants of the same fallout, suggesting the dimensions of the great regional blanket of six hundred thousand years ago, now almost wholly lost to erosion. Love said cryptically, ‘We have to assume it fell on saint and sinner alike.” It had not been milled around by streams. It was a pure ash, distinctly wind-borne, containing no sand, no clay. He said that some woolly-mammoth bones had been found not far away, and witl1 them as a minor exception this ash marked the only firm Pleistocene date in an area of twenty thousand square miles. After settling, it had zakelijke energie vergelijken not consolidated-as volcanic ash sometimes will, forming welded tuff. (The Vesuvian air-fall ash that settled on Pompeii also flew too high to weld. Rising rapidly like smoke, it actually pooled up against the stratosphere. Pliny said it looked like a flattopped Italian pine. The geologic term for such an event is “Plinian eruption.”) A couple of hundred miles northwest of us were the paint pots and fumaroles, the geysers and calderas of Yellowstone. Love said that this Lava Creek ash represented one of the great outpourings in Yellowstone history. The hail now was pelting us. It collected like roe on the brim of his Stetson. Love seemed to regard it as a form of light rain, as something that would not last even for six hundred thousand nanoseconds and was therefore beneath notice. Most zakelijke energie volcanoes and related phenomena-most manifestations of the sort represented by the surface history of Yellowstone-are lined up along boundaries of the twenty-odd plates that collectively compose the earth’s outer shell. The plates, which are something like a sixtieth of the earth’s radius, slide around on a layer of the mantle hot enough to be lubricious. Where plates spread apart (the Red Sea, the mid-Atlantic), fresh magma wells up to fill the gap. Where plates slide by one another (San Francisco, Jericho), the ground is tom and walls collapse.