The mountains

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How the mountains came up was not absolutely defined, but the story seemed clear, even if the authorship was somewhat moot, and it was a story of rhythmically successive orogenies, chapter headings in the biography of the earth. Some geologists preferred to liken them to punctuation marks, because mountain-building phases took up so little of all time-as little as one per cent, no more than ten per cent, depending on the geologist who was calculating the time. Anita conference room amsterdam said, choosing North America’s most eminent example, “The Gulf of Mexico is a big geosyncline, if you want. The big birdfoot delta of the Mississippi River is one hell of a sedimentary pile. Drill twenty-two thousand feet down and you’re still in the Eocene. The crust will take about forty thousand feet of sediment-that’s the elastic limit. Then it regurgitates the sediment, which begins to rebound. The sediment is also heated up, melted. Water, gas, and oil come out of the rock. Sedimentary layers move up with thermal drives as well as with isostasy. Sedimentary layers also move laterally, and are thus thrust sheets. In Cambra-Ordovician time, fifty million years or so before the Taconic mountains came up, the continent was to the west of us here, the coastline was in central Ohio, and to the east of us, where the Atlantic shelf is now, stood an island arc like Japan. There are volcaniclastic sediments of that age from Newfoundland to Georgia-just about the length of Japan. The present coast of Asia is the Ohio coastline in that story. Picture the sediment that is pouring off the Japanese islands into the Sea of Japan. The Martinsburg slates were shed not from the continent-not from Ohio-but conference room rotterdam mainly from the east, from the island arc offshore. You pile up forty thousand feet of sediment and it pops. The Martinsburg popped. The Taconic mountains came up. Once the process starts, it keeps itself going. You push up a mountain range, erode it into the west. The material depresses the crust. It is low-density material and it is brought down into the regime of high-density material. When enough has been piled on, the low-density material comes back up. That is how orogenic waves propagate themselves, each mountain mass being cannibalized to produce a new mountain mass to the west. But I still don’t know what started the process.”

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