The sedimentary wedge

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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.

West of Chicago

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West of Chicago and through most of Illinois, you would have been wading on clean sand, the quiet margin of the Canadian craton, which remained above the sea. The limy bottom apparently resumed in Iowa and went on into eastern Nebraska, and then, more or less at Kearney, you would have moved up onto a blistering-hot equatorial beach and into low terrain, subdued hills, rock that had been there a thousand million years. It was barren to a vengeance with a hint of life, possibly a hint of life-rocks stained green, stained red by algae. Wyoming. Past Laramie, you would have come to a west-facing beach and, after it, tidal mudflats all the way to Utah. The waters of the shelf would now begin to deepen. A hundred miles into Nevada was the continental slope and beyond it the blue ocean. If you had turned around and gone back after thirty million years-well into Ordovician time, say four hundred and sixty million years ago-the shelf edge would still have been near Elko, Nevada, and the gradually rising clean-lime seafloor would have reached at least to Salt Lake City. Across Wyoming, there may have been low dry land or possibly flexplek huren rotterdam continuing sea. The evidence has almost wholly worn away, but there is one clue. In southeastern Wyoming, a diamond pipe came up about a hundred million years ago, and, in the tumult that followed the explosion, marine limestone of late Ordovician age fell into the kimberlite and was preserved. In western Nebraska, you would have crossed dry and barren Precambrian terrain and by Lincoln have reached another sea. Iowa, Illinois, Indiana. The water was clear, the bottom uneven-many shallows and deeps upon the craton. In Ohio, the sea would have begun to cloud, increasingly so as you moved on east, silts slowly falling onto the lime. In Pennsylvania, as you approached the site of the future Delaware Water Gap, the bottom would have fallen away below you, and where it had earlier been close to the surface it would now be many tens of fathoms down. “The carbonate platform collapsed,” Anita said. “The continental shelf went flexplek huren almere down and formed a big depression. Sediments poured in.” Much in the way that a sheet of paper bends downward if you move its two ends toward each other in your hands, the limestones and dolomites and the basement rock beneath them had subsided, forming a trough, which rapidly filled with dark mud. The mud became shale, and when the shale was drawn into the heat and pressure of the making of mountains its minerals realigned themselves and it turned into slate. We moved on west a couple of miles and stopped at a roadcut of ebony slate. Anita said, “Twelve thousand feet of this black mud was deposited in twelve million years. That’s a big pile of rock.”

Within the profession

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Within the profession, the Survey had particular prestige. A geologist who sought field experience was likely to obtain it in such quantity and vaiiety nowhere else. Anita and Jack Epstein looked upon geology as “an extremely applied science” and shared a conviction that field experience was indispensable in any geological career-no less essential to a modem professor than it ever was flexplek huren rotterdam to a pick-and-shovel prospector. (“People should go out and get experience and not just tum around and teach what they’ve been taught.”) In their first year in the Survey-to an extent beyond anything they could ever have guessed-they would get what they sought. Because geology is sometimes intuitive even to the point of being subjective, the sort of field experience one happens to acquire may tend to influence one’s posture with regard to deep questions in the science. Geologists who grow up with young rocks are likely to subscribe strongly to the doctrine of uniformitarianism, whereby the present is seen to be the key to the past. They discern a river sandbar in a wall of young rock; they see a sandbar in a living river; and they know that each is in the process of becoming the other, cyclically through time. Whatever is also was, and ever again shall be. Geologists who grow up with very old rock tend to be flexplek huren almere impressed by the fact that it has been around since before the earliest development of life, and to imagine a progression in which the recycling of the earth’s materials is a subplot in a dramatic story that begins with dark scums in motion on an otherwise featureless globe and evolves through various continental configurations toward the scenery of the earth today. They refer to the earliest part of that story as “scum tectonics.” The rock cycle-with its crumbling mountains being carried to the sea to form there the rock of mountains to be -is the essence of the 1:1niformitarian principle, which was first articulated by James Hutton, of Edinburgh, at the end of the eighteenth century.

Across the valley

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Across the valley is a huge whitewash “L” on a rock above the fault scar of the Humboldt Range. We go into Sturgeon’s Log Cabin restaurant and sit down for coffee against a backdrop of rolling cherries, watermelons, and bells. A mountain lion in a glass case. Six feet to the tip of the tail. Shot by Daniel (Bill) Milich, in the Tobin Range. I hand Deffe yes the Exxon map and ask him to sketch in for me the opening of the new seaway, the spreading center as he sees it coming. “Of course, all the valleys in the Great Basin are to a greater or lesser extent competing,” he says. “But I’d put it where I said-right here.” With a pencil he begins to rough in a double line, a swath, about fifteen miles wide. He sketches it through the axis of Death Valley and up into Nevada, and then north by northwest through Basalt and Coaldale before bending due north through Walker Lake, Fallon, and Lovelock. “The spreading center would connect with a transform fault coming in from Cape Mendocino,” he adds, and he sketches such a line from the California coast to a point a little north of  flexplek huren rotterdam Lovelock. He is sketching the creation of a crustal plate, and he seems confident of that edge, for the Mendocino transform fault-the Mendocino trend-is in place now, ready to go. He is less certain about the southern edge of the new plate, because he has two choices. The Garlock Fault runs east-west just above Los Angeles, and that could become a side of the new plate; or the spreading center could continue south through the Mojave Desert and the Salton Sea to meet the Pacific Plate in the Gulf of California. “The Mojave sits in there with discontinued basin-andrange faulting,” Deffeyes says, almost to himself, a substitute for whistling, as he sketches in the alternative lines. “There has to flexplek huren almere be a transform fault at the south end of the live, expanding rift. The sea has got to get through somewhere.” Now he places his hands on the map so that they frame the Garlock and Mendocino faults and hold between them a large piece of California-from Bakersfield to Redding, roughly, and including San Francisco, Sacramento, and Fresno-not to mention the whole of the High Sierra, Reno, and ten million acres of Nevada. “You create a California Plate,” he says. “And the only question is: Is it this size, or the larger one? How much goes out to sea?” British Columbia is to his left and Mexico is to his right, beside his coffee cup on the oak Formica. The coast is against his belly. He moves his hands as if to pull all of central California out to sea.

Paleomagnetism

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“There’s more to this paleomagnetism game than reversals,” Deffeyes said, “more than just determining when, and whether, the magnetic pole was in the north or south. The earth’s magnetic field is such that a compass needle at the equator will lie flat, while a compass needle at ‘the poles will want to stand straight up on end -with all possible gradations of that in the latitudes between. So by looking at the paleomagnetic compasses in rock you can tell not only whether the magnetic pole was in the north or south when the rock formed but also-from the more subtle positions · of the needles-the latitude of the rock at tlrn time it formed.” On the striated pavement of Algeria lies the till of polar glaciers. There are tropical atolls in Canada, tropical limestones zakelijke energie in Siberia, tropical limestones in Antarctica. From fossils; from climates preserved in stone, such facts were known long before paleomagnetism was discovered; but they were, to say the least, imperfectly understood. Paleomagnetism, first perceived in igo6, eventually confirmed what the paleoclimatologists and paleontologists had been saying about the latitudes of origins of rocks, but it did not resolve the mystery of the phenomenon, because there seemed to be two equally reasonable explanations. Either the rock had moved (and continents with it) or the whole earth had rolled, like a child’s top slowly turning on its side, and the poles and equator had wandered. Either the equator had gone to Minnesota or Minnesota had gone to the equator. As early as the sixteenth century, the specific movements of the earth’s surface that eventually became known as continental drift and plate tectonics had been hypothesized. The Flemish zakelijke energie vergelijken geographer Abraham Ortelius, in the third edition of his Thesaurus Geographicus (Antwerp, i596), postulated that the American continents were “torn away from Europe and Africa” by earthquakes and other catastrophic events.

Significant alteration

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There would have been a significant alteration, however, in the demeanor of the island over the strait. At a little over two inches a year, it would have moved forty miles or so eastward, compressing the floor of the strait and pushing up high mountains, like the present mountains of Timor, which have come up in much the same way to stand ten thousand feet above the Banda Sea. Up from the sea and within those Meramecian Nevada mountains came the wine-red pebbly sandstone of the Tonka formation. Forty million years after that, when the Tonka mountains had been worn flat and the Strathearn limestones were forming over their roots, the American scene was very different. It was now the Missourian age of late Pennsylvanian time (about three hundred million years ago), and the Appalachians were still high but they were no longer alpine. Travelling west, and coming down from the mountains around Du Bois, Pennsylvania, you would have descended into a zakelijke energie densely vegetal swamp. This was Pennsylvania in the Pennsylvanian, when vegetation rioted on the earth and the big trees were kings. They were not huge by our standards but they were big trees, some with diamond patterns precisioned in their bark. They had thick boles and were about a hundred feet high. Other trees had bark like the bark of hemlocks and leaves like flat straps. Others had the fluted, swollen bases of cypress. In and out among the trunks
flew dragonflies with the wingspans of great horned owls. Amphibians not only were walking around easily but some of them had become reptiles. Through the high meshing crowns of the trees not a whole lot of light filtered down. The understory was all but woven-of rushlike woody plants and seed ferns. There were luxuriant tree ferns as much as fifty feet high. The scene suggests a tropical rain forest but was more akin to the Everglades, the Dismal Swamp, the zakelijke energie vergelijken Atchafalaya basin-a hummocky spongy landscape ending in a ragged coast. All through Pennsylvanian time, ice sheets had been advancing over the southern continents, advancing and retreating, forming and melting, lowering and raising the level of the sea, and as the sea came up and over the land in places like the swamps of Du Bois it buried them, first under beach sand and later-as the seawater deepened-under lime muds.

Extrapolation

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He had never been outside Saxony. Extrapolation was his means of world travel. He believed in “universal formations.” The rock of Saxony was, beyond a doubt, by extension the rock of Peru. He believed that rock of every kindall of what is now classified as igneous, sedimentary, and metamorphic-had precipitated out of solution in a globe-engulfing sea. Granite and serpentine, schist and gneiss had precipitated first and were thus “primitive” rocks, the zakelijke energie cores and summits of mountains. “Transitional” rocks (slate, for example) had been deposited underwater on high mountain slopes in tilting beds. As the great sea fell and the mountains dried in the sun, “secondary” rocks (sandstone, coal, basalt, and more) were deposited flat in waters above the piedmont. And while the sea kept withdrawing, “alluvial” rock-the “tertiary,” as it was sometimes called-was established on what now are coastal plains. That was the earth’s surface as it was formed and had remained. There was no hint of where the water went. Werner was gifted with such rhetorical grace that he could successfully omit such details. He could gesture toward the Saxon hills-toward great pyramids of basalt that held castles in the air…:._and say, without immediate fear of zakelijke energie vergelijken contradiction, “I hold tl1at no basalt is volcanic.” He could dismiss volcanism itself as the surface effect of spontaneous combustion of coal. His ideas may now seem risible in direct proportion to tl1eir amazing circulation, but that is characteristic more often than not of the lurching progress of science. Those who laugh loudest laugh next. And some contemporary geologists discern in Werner the lineal antecedence of what has come to be known as black-box geology-people in white coats spending summer days in basements watching million-dollar consoles that flash like northern lights-for Werner’s “first sketch of a classification of rocks shows by its meagreness how slender at that time was his practical acquaintance with rocks in the field.” The words are Sir Archibald Geikie’s, and they appeared in i905 in a book called The Founders of Geology. Geikie, director general of the Geological Survey of Great Britain and Ireland, was an accomplished geologist who seems to have dipped in ink the sharp end of his hammer. In summary, he said of Werner,

Crustal spreading

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“This is a direct result of the crustal spreading,” Deffeyes says. “It brings hot mantle up near tl1e surface. There is probably a fracture here, through which the water is coming up to this row of springs. The water is rich in dissolved minerals. Hot springs like these are the source of vein-type ore deposits. It’s the same story that I told you about the hydrothermal transport of gold. When rainwater gets down into hot rock, it brings up what it happens to find there-silver, tungsten, copper, gold. An ore-deposit map and a hot-springs map zakelijke energie vergelijken will look much the same. Seismic waves move slo lwly through hot rock. The hotter the rock, the slower the waves. Nowhere in the continental United States do seismic waves move more slowly than they do beneath the Basin and Range. So we’re not woofing when we say there’s hot mantle down there. We’ve meas1ured the heat.” The basin-range fault blocks in a sense are floating on the mantle. In fact, the earth’s crust everywhere in a sense is floating on the mantle. Add weight to the crust and it rides deeper, remove cargo and it rides higher, exactly like a vessel at a pier. Slowly disassemble I the Rocky Mountains and carry the material in small fragments to the Mississippi Delta. The delta builds down. It presses ever deeper on the mantle. Its depth at the moment exceeds twenty-five thousand feet. The heat and the pressure are so great down there zakelijke energie that the silt is turning into siltstone, the sand into sandstone, the mud into shale. For another example, the last Pleistocene ice sheet loaded two miles of ice onto Scotland, and that dunked Scotland in the mantle. After the ice melted, Scotland came up again, lifting its beaches high into the air. Isostatic adjustment. Let go a block of wood that you hold underwater and it adjusts itself to the surface isostatically. A frog sits on the wood. It goes down. He vomits. It goes up a little. He jumps. It adjusts. Wherever landscape is eroded away, what remains will rise in adjustment. Older rock is lifted to view. When, for whatever reason, crust becomes thicker, it adjusts downward. All of this-with the central image of the basin-range fault blocks floating in the mantle-may suggest that the mantle is molten, which it is not.

The road builders

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Geologists on the whole are inconsistent drivers. When a roadcut presents itself, they tend to lurch and weave. To them, the roadcut is a portal, a fragment of a regional story, a proscenium arch that leads their imaginations into the earth and through the surrounding terrane. In the rock itself are the essential clues to the scenes in which the rock began to form-a lake in Wyoming, about as large as Huron; a shallow ocean reaching westward from Washington Crossing; big rivers that rose in Nevada and fell through California to zakelijke energie the sea. Unfortunately, highway departments tend to obscure such scenes. They scatter seed wherever they think it will grow. They “hair everything over” -as geologists around the country will typically complain. “We think rocks are beautiful. Highway departments think rocks are obscene.” “In the North it’s vetch.” “In the South it’s the god-damned kudzu. You need a howitzer to blast through it. It covers the mountainsides, too.” “Almost all our stops on field trips are at roadcuts. In areas where structure is not well exposed, roadcuts are essential to do geology.” “Without some roadcuts, all you could do is drill a hole, or find natural streamcuts, which are few and far between.”
“We as geologists are fortunate to live in a period of great road building.” “It’s a way of sampling fresh rock. The road builders slice through indiscriminately, and no little rocks, no softer units are allowed to hide.” “A roadcut is to a geologist as a stethoscope is to a doctor.” “An X-ray to a dentist.” “The Rosetta Stone to an Egyptologist.” “A twenty-dollar bill to a hungry man.” “If I’m going to drive safely, I can’t do geology.” In moist climates, where vegetation veils the earth, streamcuts are about the only natural places where geologists can see exposures of rock, and geologists have walked hundreds of thousands of miles in and beside streams. If roadcuts in the moist world zakelijke energie vergelijken are a kind of gift, they are equally so in other places. Rocks are not easy to read where natural outcrops are so deeply weathered that a hammer will virtually sink out of sight-for example, in piedmont Georgia. Make a fresh roadcut almost anywhere at all and geologists will close in swiftly, like missionaries racing anthropologists to a tribe just discovered up the Xingu.

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