The sedimentary wedge

Gerelateerde afbeelding

The sedimentary wedge that has come off the Rockies is thickest there by the mountain front, and gradually thins to the east. Kansas and Nebraska are like pieces cut from a wheel of cheese-lying on their sides, thick ends to the west. Altitude in itself suggests the volume of material. Kansas and Nebraska are three thousand feet higher in the west than in the east. We were running on the summits of the Poconos-uneven but essentially level topography, the Pocono equivalent of Alpine minarets. Where we saw stratified rock in roadcuts, it seemed level enough to stop a bubble. For the most part, it was Catskill sandstone, red as borscht, from latest Devonian and earliest Mississippian time. The summits of the Poconos were not only cragless, they ran on under the scrub oaks as far as the eye could see. There were peat bogs. There was a great deal of standing water. The landscape was bestrewn with hummocky lumps of gravel. “There’s no way that streams brought all that co-working space rotterdam gravel up here,” Anita said. “Religious farmers say it’s evidence of the Great Flood.” If so, the Great Flood was frozen. These were morainal gravels, outwash gravels. Interstate 80 marks almost exactly the Wisconsinan ice sheet’s line of maximum advance in the Poconos.
We made a short digression from the interstate to see-in some Devonian siltstone-a tidal flat that was stuffed with razor clams. The surface of the rock had a Fulton Market look. It was a pai5ley of conglomerate clams. Three hundred and seventy-five million years old, they resembled exactly their modem counterparts. “Things haven’t changed much,” Anita said as she got back into the car. We drove on into Hickory Run State Park, where we walked through heavy woods toward a clear space ahead. We seemed to be approaching a body of co-working space almere water. Its edge resembled a shore, and its seventeen acres were surrounded by conifers, whose jagged silhouettes invoked a northern pond. In place of water, however, the pond consisted of boulders-thousands of big boulders, some of them thirty feet long, nearly all of them red rock weathered dusty rose, and all of them accordant with a horizontal plane, causing them to seem surreally a lake of red boulders. DAD, MOM, HARRY, and GEORGE had been there in i970 with a can of acrylic spray. JOE VIZZARD came some years later. Dozens of others had daubed the rocks on days ranging backward to i935, when the park was established. The big red-boulder expanse was difficult to cross, however, and its sorry guestbook was confined to one comer. The boulders were stunningly beautiful-in their lacustrine tranquillity, their lovely color, their spruce-rimmed absence of all but themselves. We walked out some distance, stepping from one to another multiton red potato.