Cambrian sandstone

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Some remnant Cambrian sandstone formed a blister in the valley. The interstate drifted around it in a westerly way and toward the foot of still another endless mountain-Bald Eagle, the last ridge of the deformed Appalachians. After the Cambrian sandstone, the Ordovician dolomite, there was Silurian quartzite in the gap that broke through the mountain. Its strata dipped steeply west. The rock had bent again, and again we were moving upward through history. Now, though, the dip of the strata would reverse no more. In a dozen miles of ever younger rock, we climbed through the Paleozoic era almost from beginning to end. We went up through time at least three hundred million years and up through the country more than a co-working space almere thousand vertical feet, the last ten miles uphill all the way, from Bald Eagle Creek to Snow Shoe, Pennsylvania-the longest steady grade on I-80 east of Utah-while light, wind-driven snow began to fall. We had come to the end of the physiographic province of the folded-and-faulted mountains, and the long ascent recapitulated Paleozoic history from the clean sands of the pre-tectonic sea to the dense twilight of Carboniferous swamps. We came up through the debris of three cordilleras, through repetitive sandstones and paper shales-Silurian paper shales, Devonian paper shales, Mississippian paper shales-crumbling on their shelves like acid-paper books in libraries. The shales were so incompetent that they would long since have avalanched and buried the highway had they not been benched-terraced in the manner of Machu Picchu. In other roadcuts, Catskill Delta sandstones, beet-red and competent, were sheer. We had gone through enough hard co-working space amsterdam ridges and soft valleys for me not just to sense but to see the Paleozoic pageant repeatedly played in the rock. For all the great deformity and complexity, the mountains now gone had left patterns behind. The land rising and falling, the sea receding and transgressing, the ancestral rivers losing power through time had not just obliterated much of what went before but had always imposed new scenes, and while I, for one, could not hold so many hundreds of pictures well related in my mind I felt assured beyond doubt that we were moving through more than chaos. The strata at the foot of the ten-mile hill had been nearly vertical. Gradually, through the long climb, they levelled out. They leaned backward, relaxed, one degree every two million years, until in the end they were Rat-at which moment the interstate left the deformed Appalachians and itself became level on the Allegheny Plateau.

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