Annals of the Former World

by John McPhee

  If you could have travelled westward from the site of Chicago eleven hundred million years before the present, you would have traversed, along the modern route of Interstate 80, most of what geologists now see in the Precambrian basement. In Illinois, you would have been among the bevelled rhyolites and buried granites of the once high and Andean continental margin. In eastern Iowa, you would have crossed a plutonic belt, also bevelled by erosion, dating from the anorogenic perforation of North America.

  If you could have come the other way, also on I-80, eleven hundred million years ago, you would have passed through the sites of Rock Springs and Rawlins on the worn-down shield rock of the Archean Wyoming craton. Near Laramie—after running along and then jumping across the old Cheyenne Belt, edge of the continent in 1800—you would have moved onto the compacted island-arc complex whose dockings filled in Colorado and Nebraska, and much of the rest of the United States. You would not have encountered there the pink granite (today’s front-range granite) that came into the arc complex around 1450 as one of the mysterious plutons. It was still buried too deep. On post-1800 metavolcanic rock, you would have continued across Nebraska through North Platte and Kearney to Lincoln.

  These eleven-hundred-million-year-old North American time lines have now all but met in the middle—at the future sites of Lincoln, Omaha, Des Moines. In 1108, when the rifting began, the three sites were a good deal closer together. Now, around 1100, they were still moving apart and would continue to move apart for fourteen million years. Something under the core of North America was tearing North America apart, threatening its continuing existence as an integral continent. It seems likely that the cause of the Midcontinent Rift was a thermal plume from deep in the mantle, a geophysical hot spot doming the crust and then cracking it. Flood basalts filled the rifting valley. At night above the lava fountains the whole sky was red. At about 1100, the triple junction broke open under Lake Superior, connecting this southwestern arm and the arm that ran through Michigan. If the rifting had gone on long enough, the country between the two active arms—including at least half of what is now called the Midwest—would have departed from North America to end up who knows where and in how many pieces. In the middle of North America, a great bay would have developed, with a shoreline of a thousand miles.

  Between Lincoln and Omaha, I-80 runs directly over the center of the rift. It gradually slides toward the rift’s eastern flank at Des Moines. On I-80, the whole western half of Iowa is over the rift itself or its flanking basins. To follow this cartographically, you would need the Composite Magnetic Anomaly Map or an isostatic residual gravity map of the United States. On the magnetic and gravity maps the Midcontinent Rift is the most prominent feature you see. A quarter-century ago, it was as unknown in scientific mapping as it still is in road mapping. It was referred to as “the midcontinent gravity anomaly” or “the midcontinent gravity high”—descriptions merely, without implication or sense of cause. If the rifting had continued even for a couple of hundred million years, as the Mid-Atlantic rifting has done, Lincoln and Des Moines would be as far apart as Jersey City and Casablanca, whose sites were once as close as Lincoln and Des Moines. Yet that did not happen. The midcontinent rift system did not in the end play a major role in the evolution of the continent, because the rifting stopped—or was stopped—more or less abruptly. The rift system’s oldest rocks date from 1108, the youngest from 1086, so the rifting lasted twenty-two million years—not much by comparison with an Atlantic Ocean, but (to date) about three times the rifting of the Gulf of California and longer than the rifting of the Red Sea.

  Something seems to have snuffed out the young hot spot, leaving the midcontinent intact. Where crustal blocks had dropped in the middle of the rift as it widened, they now were subjected to a compressional force so great that the middle of the rift rose up to a position higher than the sides. In the language of geology, grabens were squeezed upward and became horsts. It was as if the Red Sea were to stop widening, while its floor came up to stand higher than the shores. The compressional force that stopped the rift in Proterozoic North America is believed to have been the Grenville Orogeny. This name has been given to a continent-to-continent collision, completed by about 1050, that brought the West African Craton and the Amazonian Craton against the eastern and southern margins of North America to create the supercontinent Rodinia, hundreds of millions of years before Pangaea, the most recent of supercontinents. In Grenville time, the African and South American cratons were neither configured nor juxtaposed as they would be in the next eon. They were not put together as they are now. They resembled their modern forms about as little as North America did. From Texas to Labrador, the Grenville Orogeny built the beginnings of eastern America.

  As a kind of exclamation point at the end of these events, an isolated plume under Colorado seems related to the Grenville Orogeny. Dating from the same time as the continent-to-continent collision and the stopping of the rift, a batholith intruded Colorado, its presence otherwise inexplicable. Nothing else was happening, or was about to happen, in or near Colorado at that time. Then suddenly appeared this maverick granite—the granite of Pikes Peak—distinct in age and texture from all other Rocky Mountain granites. In Van Schmus’s words, “It cooled off, and that was it. The Pikes Peak batholith just sits out there all by its lonesome.” After that—to the end of the Precambrian—the midcontinent was quiet for half a billion years.

  A Narrative Table of Contents

  In 1978, I began a series of journeys across the United States in the company of geologists, with the purpose of doing a piece of writing that would describe not only the rock exposed in roadcuts but the geologists with whom I travelled. The result was meant to be a sort of cross section of North America at about the fortieth parallel, and a picture of the science. On (and away from) Interstate 80, I travelled for a year, sometimes traversing the country all the way, but generally covering a segment with this or that geologist—with Professor Kenneth Deffeyes, of Princeton University; with the sedimentologist Karen Kleinspehn, then a Princeton graduate student and now a professor at the University of Minnesota; with Anita Harris, of the United States Geological Survey; with David Love, of the Survey; and with the tectonicist Eldridge Moores, of the University of California, Davis. At the end of that first series of trips, after I transcribed my notes and developed a structure for the over-all composition, I discovered that I had outlined something that would keep me writing for more years than I wanted to spend consecutively on the subject. The structure had four main sections, which stood apart as well as together, so I decided to write them at intervals, always turning to other fields before returning to geology and to more wanderings with the respective geologists. The additional travel led as far away from Interstate 80 as mainland Greece, the island of Cyprus, a mining camp in Arizona, and the San Andreas Fault from end to end. The topic reached beyond the American cross section into world ophiolites and global tectonics. It somehow involved Robert Louis Stevenson, Chief Washakie, and Theodore Roosevelt (twice). It somehow involved Winona of the Lenape, William Tecumseh Sherman, William Penn, and Johann Augustus Sutter.

  The controlling element—the theme that guided the basic structure—was plate tectonics. The plate-tectonics revolution had occurred in the nineteen-sixties, and when I set out on my travels the concept was not without detractors. I wanted to see who was opposed, and why, and in what ways the new theory was being tested and applied. There would be plenty of other matters discussed, but plate theory was paramount. The structure is not linear—not a straightforward trip from New York to San Francisco on the interstate. It jumps about the country. For example, it begins in New Jersey and leaps to Nevada, because the tectonics in New Jersey two hundred million years ago are being recapitulated by the tectonics in Nevada today.

  Now, with its completion, the project represents the stratum of time 1978–1998. Its first four components were published in 1981, 1983, 1986, and 1993. A fifth and final essay appears in this volume to fill
a significant gap. Nowhere in the structure I have referred to was there much of anything about the midcontinent. It was there in a broad and general way. It was there in a number of time lines shot across the country in various periods, epochs, and ages. But it was not there in any kind of rock-to-rock progression. In mid-America, there are few surface rocks. That initial over-all composition, purporting to traverse the nation, deliberately overlooked a large piece of the nation—Chicago to Cheyenne. If the rocks were scarce, the tectonics were scarcer. For more than a billion years, little to nothing had happened there. Even so, I felt a measure of guilt about the omission, and contemplated what to do to close that epic caesura. The answer came with the geophysical insights of recent years, the combined advances in many fields, from radiometric dating to computer science, that have enabled geologists to see the midcontinent itself forming and developing in the Precambrian eons. This was the basement of the world, under construction. I thought it a good idea to travel between Cheyenne and Chicago down there. I did so, in a way, with W. R. Van Schmus, of the University of Kansas.

  Because the entire composition in all its parts was written in the form of journeys, set pieces, flashbacks, biographical sketches, and histories of the human and lithic kind—intended as an unfolding piece of writing and not as a catalogue of geologic topics—the text firmly refrained from offering a way in which a reader could easily turn to something like the basic set piece on plate theory or the basic set piece on geologic time. In the interest of the composition, such topics were not discretely labelled. That is why I am writing a narrative table of contents. In this inclusive volume, I am trying to have things both ways. While leaving the text unparcelled and continuous, I want to explain up front not only how the project came to be, and how it evolved across the twenty years, but also what’s what and where.

  Basin and Range, as the opening story, is the primer. It contains the long set piece on the nature and history of plate tectonics—what it is, who figured it out, and how.

  Basin and Range also includes the long set piece on time. The time scale we more or less take for granted did not exist in the early nineteenth century. In fifty years or so, it was gradually assembled by amateurs (often medical doctors) who pieced this to that, saw which came earlier, and gave names to distinctive zones of time. As you try to follow the changing face of the earth, the role of time is of course all-important, and time in its quantity is very hard to sense.

  In college, I majored in English. In college and in high school, I took various introductory courses in physics, chemistry, biology, and geology, but only out of idle interest or to discharge distributional requirements. Like all writing, writing about geology is masochistic, mind-fracturing self-enslaved labor—a description that intensifies when the medium is rock. What then could explain such behavior? Why would someone out of one culture try to make prose out of the other? Why would someone who majored in English choose to write about rocks? Why would a person who works for something called a Humanities Council and teaches a university course called Humanistic Studies 440 undertake to write about geology? I believe those questions are answered in one paragraph from Basin and Range.

  With brief exceptions, I have lived all my life in Princeton, New Jersey, where I was educated in the public schools and at the university. When I was seventeen, I went off to Deerfield Academy, in Massachusetts, where a geologist named Frank Conklin presented his subject in a first-rate full-year course. Even then, I was an English-major designate, but in the decades of writing that followed—highly varied non-fiction writing, often involving natural scenes—the geology lay there to be tapped. Sooner or later in many of my projects, geology would be touched upon in one way or another, and I would ask the geologists of the Princeton faculty to help me get it right. There were some geological passages in books like The Pine Barrens and Encounters with the Archdruid, for example, and there were more in Coming into the Country, arising from a question I had long meant to ask. Obviously, the placer gold in the drainages of the Yukon was there because weather had broken up mountains and bestrewn the gold in the gravels of streams. That I thought I understood. But I wondered what had put the gold in the mountains in the first place. I called the Geology Department and talked with a professor who said he could not begin to answer the question. He had a preoccupying interest in Jurassic leaves. “Call Ken Deffeyes,” he said. “Deffeyes knows, or thinks he knows.” For me, Deffeyes put the gold in the mountains.

  A year or so later, in a random conversation with this same eclectic petrologue, I asked if he thought we might find a Talk of the Town piece for The New Yorker in a roadcut near the city. We could look at the blast-exposed face of the rock, read its history, and tell it in the first-person plural. While we were still planning this short trip, I asked him if there would not be an even better story in a journey north from roadcut to roadcut—for example, up the Northway’s stunning route through the Adirondacks.

  “Not on this continent,” said Deffeyes. “If you want to do that sort of thing on this continent, go west—go across the structure.”

  In one moment, bounding and rash, my thoughts raced to San Francisco with roadcuts lining the route like billboards, each with its own message. “Why not go all the way?” I said to him. Two weeks later, we were looking for silver in Nevada.

  Deffeyes has stood beside this project for twenty flattering years, always seeming to assume that my comprehension and capabilities are twice their actual size, never showing the slightest sign of stress, or even awareness, when he is talking six to eight metres above my head. As widely read as if he were a professor of comparative literature, he intuitively understood the goal I had set up: to present his science and its practitioners in a form and manner that was meant to arrest the attention of other people while achieving acceptability in the geologic community. I was naive even to think of such a thing, and a nervous wreck for months on end, but I learned a lot in twenty years. Deffeyes searched his mind and the geologic literature, and suggested—for the Appalachians, the Rocky Mountains, and California—geologists I might travel with. He called them, interested them in what I was trying to do, and asked if they would help. Since I travelled with all of them in that first year, they in turn became twenty-year counsellors as well as companions.

  Several transcontinental time lines are drawn at selected moments in the text—glimpses of paleogeography, sweeping pictures of the United States as it appeared at some far gone date in the former world. There is a late Triassic journey in Basin and Range, and time lines from the Mississippian and Pennsylvanian periods are a part of the deep-time set piece. As a way of introducing the idea of time lines, Basin and Range first presents a rapid transcontinental traverse through the physiographic provinces of the here-and-now. In In Suspect Terrain, there’s a Cambrian and Ordovician pair, and a pair from the Silurian. The earliest plants to appear on land came after the first and before the second of those Silurian time lines. In Rising from the Plains, an Eocene time line starts from both east and west and meets in a huge lake in what is now Wyoming.

  After Basin and Range deals with plate theory in presentational fashion, Anita Harris, of In Suspect Terrain, in several ways attacks it.

  In Suspect Terrain was constructed in four panels: 1. the biography of Anita Harris; 2. the Delaware Water Gap as a fragment of the Appalachians (understand a fragment and you’ll have gone a long way toward understanding the whole); 3. the Appalachians and plate tectonics; 4. the theory of continental glaciation (used here to contrast its lack of acceptance in the nineteenth century with the experience of plate theory in the twentieth). The four panels are not presented as such, but they are distinct for anyone who cares to notice. Note the gap between 244 and 254. It contains short set pieces on coal and petroleum. The narrative, at that point, is in western Pennsylvania, and western Pennsylvania is a prime place to go into both of those subjects. The Delaware Water Gap panel is a freestanding experiment, a composition within a composition. Human history there (a few t
housand years) is set in duet with the geologic history, to help make some sort of point. The ambition of the text relates closely to the George Inness painting. Tell me what made that scene and you will tell me what made the eastern United States. Look over the shoulder of the painter and see how it was done.

  Geologists write “terrain” when they mean topography and “terrane” when they are referring to a piece of country many miles deep. When I first published In Suspect Terrain, I wrote, “I am not a geologist and I refuse to cooperate.” Terrane, actually, has been a word in the English language at least since the mid-nineteenth century. Webster knows what it means. But I had not so much as looked it up, and I was bullheaded, savoring the ambiguities that danced around the single spelling. I now have a changed mind, an improved attitude. Terrain is topography. Terrane is a large chunk of the earth, in three dimensions. I have changed the text wherever necessary. My last-ditch holdout position, though, is the title In Suspect Terrain. It stays, retaining its meanings.

  Anita Harris grew up in the Williamsburg section of Brooklyn and frankly went into geology in order to get out of the city. Within the profile of her is a profile of New York City geology. Her international reputation is mainly the result of paleontological discoveries that have enhanced the search for oil. I accompanied her as she collected carbonate rocks from New Jersey to Indiana. In the context of Appalachian history—among mountains that are thought by many to represent the suturing of two continents—her cautionary remarks about plate theory are given unrestrained expression.