by John McPhee
It stands at the surface of a huge piece of country. Erosion working into the high eastern end has cut the shapes of the Catskill Mountains. The rock lies essentially flat there, and is flat all the way to the shores of Lake Erie. It is the uppermost rock of half of New York State. It is the rock of Chenango, the rock of Chautauqua, too. It is the rock of Seneca, Ithaca, Elmira, Oneonta. In Pennsylvania, it is largely buried, or was sliced and kneaded into the deformed mountains, but as the so-called Poconos it stands flat and high. The Poconos actually are part and parcel of the New York Devonian clastic wedge. The Poconos are a tongue of New York State penetrating Pennsylvania.
The Acadian mountains are gone. The wedge remains. The Acadians, in their Devonian prime, must have been a crowd of Kanchenjungas, to judge by their sedimentary remains, which reach almost to Indiana. As the mountains came down, they stood ever deeper in debris. At Denver, the Rocky Mountains are up to their hips in their own waste. 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 Poeonos—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 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 paisley of conglomerate clams. Three hundred and seventy-five million years old, they resembled exactly their modern 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 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 1970 with a can of acrylic spray. JOE VIZZARD came some years later. Dozens of others had daubed the rocks on days ranging backward to 1935, when the park was established. The big red-boulder expanse was difficult to cross, however, and its sorry guestbook was confined to one corner. 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.
Anita lost her balance and almost went below. “What a klutz,” she remarked.
I thought I might be learning a geologic term.
“These are periglacial boulders,” she went on. “They’re not erratics. They haven’t really moved. In the climates we have now, big boulders that are not erratics just don’t appear in the woods. Only a remarkable set of conditions would produce this scene. You had to start with the right bedrock. You had to have the right angle of dip, the right erosional shape for flushing, the right distance from the glacier. The terminus of the glacier was about half a mile away. The climate was arctic. Imagine the frost heaves after water in summer got into the bedrock and that kind of winter came to explode it. Gravels, sands, and clay were completely flushed away by melt-water, leaving these boulders.”
Twenty-five thousand years ago—in the late Pleistocene, or, relatively speaking, the geologic present—arctic frost had broken out the boulders and had begun the weathering that rounded them. The Acadian mountains, wearing away three hundred and fifty million years ago, had provided the material of which the boulders were made. Back on the interstate and continuing across the Pocono Plateau, we ran through more flat-lying red strata of the same approximate age, and Anita said, “Remember the Bloomsburg? This rock is fifty million years later, and it looks like the Bloomsburg, and it was formed on another low, alluviated coastal plain, when the Acadian mountains were dying down. As I’ve been telling you, geology is predictable once you learn a few facts. Geology repeats itself all through the rock column.”
On the geologic time scale, anyone could assign these events to their respective places and sense the rhythms of the cycles—rock cycles, glacial cycles, orogenic cycles: overlapping figures in the rock. Taken all together, though, they seemed to ask somewhat more than they answered, to reveal less than nature kept concealed. The evidence showed that the Acadian mountains had come down, as had the Taconics before them, and each had spread westward new worlds of debris. One could also discern that the Acadian Orogeny had folded and faulted the sedimentary rock that had formed from the grit of the earlier mountains, and metamorphosed the rock as well—changed the shales into slates, the sandstones into quartzites, the limestones and dolomites into marble. A third revolution would follow—the Alleghenian Orogeny, in Pennsylvanian-Permian time. Another mountain wave would crest, break, and send its swash to westward. It was all very repetitive, to be sure—the great ranges rising, falling, rising, falling, covering and creating landscapes, as if successive commingling waters were to rush up a beach and freeze. But why? How? You see in rock that geology repeats itself, but you do not see what started the process. In the rivers in rock you find pieces of mountains, but you do not find out why the mountains were there.
I said to Anita, “What made the mountains rise?”
“The Acadian mountains?”
“All of them—Taconic, Acadian, Alleghenian. What made them come up in the first place?”
It has been Anita’s style as a geologist to begin with an outcrop and address herself to history from there—to begin with what she can touch, and then to reason her way back through time as far as she can go. A river conglomerate, as tangible rock, unarguably presents the river. The river speaks of higher ground. The volume of sediment that the river has carried can imply a range of mountains. To find Precambrian jaspers in the beds of younger rivers means that the Precambrian, the so-called basement rock, was lifted to form the mountains. These are sensible inferences drawn cleanly through an absence of alternatives. To go back in this way, retrospectively, from scene to shifting scene, is to go down the rock column, groping toward the beginning of the world. There is firm ground some of the way. Eventually, there comes a point where inference will shade into conjecture. In recesses even more remote, conjecture may usurp the original franchise of God.
By reputation, Anita is a scientist with an exceptionally practical mind, a geologist with few weaknesses, who is at home in igneous and metamorphic petrology no less than in sedimentology. She has been described as an outstanding biostratigrapher, a paleontologist who knows the rocks in the field and can go up to a problem and solve it. In my question to her, I was, I will confess, rousing her a little. I knew what her answer would be. “I don’t know what made the mountains come up in the first place,” she said. “I have some ideas, but I don’t know. The plate-tectonics boys think they know.”
When the theory of plate tectonics congealed, in the nineteen-sixties, it had been brought to light and was stro
ngly supported by worldwide seismic data. With the coming of nuclear bombs and limitation treaties and arsenals established by a cast of inimical peoples, importance had been given to monitoring the earth for the tremors of testing. Seismographs in large numbers were salted through the world, and over a decade or so they revealed a great deal more than the range of a few explosions. A global map of earthquakes could be drawn as never before. It showed that earthquakes tend to concentrate in lines that run up the middles of oceans, through some continents, along the edges of other continents—seamlike, around the world. These patterns were seen—in the light of other data—to be the outlines of lithospheric plates: the broken shell of the earth, the twenty-odd pieces of crust-and-mantle averaging sixty miles thick and varying greatly in length and breadth. Apparently, they were moving, moving every which way at differing speeds, awkwardly disconcerting one another—pushing up alps—where they bumped. Coming apart, they very evidently had opened the Atlantic Ocean, about a hundred and eighty million years ago. Where two plates have been moving apart during the past twenty million years, they have made the Red Sea. Ocean crustal plates seemed to dive into deep ocean trenches and keep on going hundreds of miles down, to melt, with the result that magma would come to the surface as island arcs: Lesser Antilles, Aleutians, New Zealand, Japan. If ocean crust were to dive into a trench beside a continent, it could lift the edge of the continent and stitch it with volcanoes, could make the Andes and its Aconcaguas, the Cascade Range and Mt. Rainier, Mt. Hood, Mt. St. Helens. It was a worldwide theory—revolutionary, undeniably exciting. It brought disparate phenomena into a single story. It explained cohesively the physiognomy of the earth. It linked the seafloor to Fujiyama, Morocco to Maine. It cleared the mystery from long-known facts: the glacial striations in rock of the Sahara, the equator’s appearances in Fairbanks and Nome. It was a theory that not only opened oceans but closed them, too. If it tore land apart, it could also suture it, in collisions that perforce built mountains. Italy had hit Europe and made the Alps. Australia had hit New Guinea and made the Pegunungan Maoke. Two continents met to make the Urals. India, at unusual speed, hit Tibet. Eras before that, South America, Africa, and Europe had, as one, hit North America and made the Appalachians. The suture was probably the Brevard Zone, a long, northeast-trending fault zone in the southern Appalachians with very different rock types on either side and no discernible matchup of offset strata. Discontinuous extensions of the Brevard Zone seemed to reach to the Catoctin Mountains and on to Staten Island. Southeastern Staten Island apparently was a piece of the Old World. Ships that sailed for Europe had arrived when they went under the bridge.
Plate theory was constructed in ten years by people with hard data who were consciously and frankly waxing “geopoetical” as well. Once the essentials of the theory were complete—after the discovery of seafloor spreading had led to an understanding of trench subduction, and after the plates and their motions had finally been outlined and described—the theory took a metaphysical leap into the sancta of the gods, flaunting its bravado in the face of Yahweh. It could make a scientist uncomfortable. Instead of reaching back in time from rock to river to mountains that must have been there—and then on to inference and cautious conjecture in the dark of imperceivable unknowns—this theory by its conception, its nature, and its definition was applying for the job of Prime Mover. The name on the door changed. There was no alternative. The theory was panterrestrial, panoceanic. It was the past and present and future of the world, sixty miles deep. It was every scene that ever was on earth. Either it worked or it didn’t. Hoist it was to heaven with its own petard. “Established” there, it looked not so much backward from the known toward the unknown as forward from the invisible to its product the surface of the earth. Anita was more worried than made hostile by all this. By no means did she reject plate theory out of hand. There were applications of it with which she could not agree. Moreover, it was too fast a vehicle for its keys to be given to children.
“The plate-tectonics people have certain set patterns that they expect to see,” Anita said. “They kind of lock themselves in. If something doesn’t fit the theory, they’ll find some sort of reason. They’ll say that something is missing, or that it was subducted, or that it has not yet been found in the subsurface. They make things fit.”
“Do you believe that ocean crust is subducted into trenches, that it melts and then comes up behind the trenches as volcanoes and island arcs?” I asked her.
“That is straightforward,” she said. “And I have no doubt that one edge of the Pacific Plate is grinding northwest through California. What I object to is plate tectonics taken as absolute gospel. To stuff that I know about, it’s been overapplied—without attention to geologic details. It’s been misused terribly. It has misrepresented facts. It has oversimplified the world. The Atlantic spreading open I absolutely believe. How long it has been spreading open I don’t know. I don’t really believe that North America and South America were up against one another. The whole Pacific margin is thrusting from west to east, but there is no continent colliding with it. I don’t see that plate tectonics explains all of these things. I think tectonics on continents is different from tectonics in oceans, and what works in oceans is often misapplied on land. As a result, there is less understanding of regional geology. The plate-tectonic model is so generalized and is used so widely that people do not get good regional pictures anymore. People come out of universities with Ph.D.s in plate tectonics and they couldn’t identify a sulphide deposit if they fell over it. Plate tectonics is not a practical science. It’s a lot of fun and games, but it’s not how you find oil. It’s a cop-out. It’s what you do when you don’t want to think.”
Before the plate-tectonics revolution, back in the penumbra of the Old Geology, mountains (as has been noted) were thought to be driven upward from a deep-seated source known as a geosyncline—a profound downwarp of the crust, a long trough below the sea, which sediments fell into. East of North America, for example, the muds that would become Martinsburg slates first became rock in a geosyncline. The great trough trended northeast, like the mountains it would produce. 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 said, choosing North America’s most eminent example, “The Gulf of Mexico is a big geosyncline, if you want. The big bird-foot 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 Cambro-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 New-foundland 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 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-de
nsity 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.”
Historical geologists, in the olden days, pieced together that narrative. Economic geologists, in their pragmatic way, cared less. In describing the minable Martinsburg—the blue-gray true unfading slate—C. H. Behre, Jr., wrote in 1933, “Sedimentary rocks are often compressed from the sides through what may be loosely described as shrinking of the crust of the earth; how this shrinking is brought about is, for the present purpose, beside the point. It has the well-recognized effect, however, that layers or bedding planes are wrinkled or thrown into ‘folds.’”
By the nineteen-seventies, what Behre had loosely described was widely believed to be the impact of one continent colliding with another, as Iapetus, the proto-Atlantic ocean, was closed and the suture of the two continents became the spine of the Appalachians. The successive pulses of orogeny—Taconic, Acadian, Alleghenian—were attributed to the irregular shapes of shelves and coastlines of the continents. Where they bulged, the action would have an early date, and especially where some cape, point, or peninsula had a similar feature coming from the opposite side. Such headlands, in advance contact, were said to have produced the Taconic Orogeny. Great bays, eventually coming against one another, set off the Acadian Orogeny. The Alleghenian Orogeny was the final crunching scrum, completing the collision. The apparent suture was a line running through Brevard, North Carolina, more or less connecting Atlanta, Asheville, and Roanoke, not to mention Africa and America.
