by John McPhee
Book 2
In Suspect Terrain
Detail from “Delaware Water Gap,” by George Innes, 1859. Collection of the Montclair Art Museum
The paragraph that follows is an encapsulated history of the eastern United States, according to plate-tectonic theory and glacial geology.
About a thousand million years ago, a continent of unknown dimensions was rifted apart, creating an ancestral ocean more or less where the Atlantic is now. The older ocean has been called Iapetus, because Iapetus was the father of Atlas, for whom the Atlantic is named. Some geologists, who may feel that their science is dangerously clever, are snappish about Iapetus. They prefer to say proto-Atlantic. The ancestral ocean existed a great deal longer than the Atlantic has, but gradually, across some two hundred and fifty million years in the Paleozoic era, it closed. Moving toward each other, the great landmasses on either side buckled and downwarped the continental shelves and then came together in a crash no less brutal than slow—a continent-to-continent collision marked by an alpine welt, which has reached its old age as the Appalachian Mountains. In the Mesozoic era, two hundred and ten million years ago, rifting began again, pulling apart certain segments of the mountain chain, creating fault-block basins—remnants of which are the Connecticut River Valley, central New Jersey, the Gettysburg battlefields, the Culpeper Basin—and eventually parting the earth’s crust enough to start a new ocean, which is now three thousand miles wide and is still growing. Meanwhile, a rhythm of glaciation has been established in what is essentially the geologic present. Ice sheets have been forming on either side of Hudson Bay and have spread in every direction to cover virtually all of Canada, New England, New York, and much of New Jersey, Pennsylvania, and the Middle West. The ice has come and gone at least a dozen times, in cycles that seem to require about a hundred thousand years, and, judging by other periods of glaciation in the earlier history of the earth, the contemporary cycles have only begun. About fifty more advances can be expected. Some geologists have attempted to isolate the time in all time that runs ten thousand years from the Cro-Magnons beside the melting ice to the maternity wards of the here and now by calling it the Holocene epoch, with the implication that this is our time and place, and the Pleistocene—the “Ice Age”—is all behind us. The Holocene appears to be nothing more than a relatively deglaciated interval. It will last until a glacier two miles thick plucks up Toronto and deposits it in Tennessee. If that seems unlikely, it is only because the most southerly reach of the Pleistocene ice fields to date stopped seventy-five miles shy of Tennessee.
Anita Harris is a geologist who does not accept all that is written in that paragraph. She is cool toward aspects of plate tectonics, the novel theory of the earth that explains mountain belts and volcanic islands, ocean ridges and abyssal plains, the deep earthquakes of Alaska and the shallow earthquakes of a fault like the San Andreas as components of a unified narrative, wherein the shell of the earth is divided into segments of varying size, which separate to form oceans, collide to make mountains, and slide by one another causing buildings to fall. In a revolutionary manner, plate-tectonic theory burst forth in the nineteen-sixties, and Anita Harris is worried now that the theory is taught perhaps too glibly in schools. In her words: “It’s important for people to know that not everybody believes in it. In many colleges, it’s all they teach. The plate-tectonics boys move continents around like crazy. They publish papers every year revising their conclusions. They say that a continental landmass up against the eastern edge of North America produced the Appalachians. I know about some of the geology there, and what they say about it is wrong. I don’t say they’re wrong everywhere. I’m open-minded. Too often, though, plate tectonics is oversimplified and overapplied. I get all heated up when some sweet young thing with three geology courses tells me about global tectonics, never having gone on a field trip to look at a rock.”
As she made these comments, she was travelling west on Interstate 80, approaching Indiana on a gray April morning. She had brought me along to “do geology,” as geologists like to say—to see the countryside as she discerned it. Across New Jersey, Pennsylvania, and Ohio, she had been collecting, among other things, limestones and dolomites for their contained conodonts, index fossils from the Paleozoic, whose extraordinary utility in oil and gas exploration had been her discovery, with the result that Mobil and Chevron, Amoco and Arco, Chinese and Norwegians had appeared at her door. She was driving, and she wore a railroad engineer’s striped hat, a wool shirt, blue jeans, and old split hiking boots—hydrochloric acid for testing limestones and dolomites in a phial in a case on her hip. With her high cheekbones, her assertive brown eyes, her long dark hair in twin ponytails, she somehow suggested an American aborigine. Of middle height, early middle age, she had been married twice—first to a northern-Appalachian geologist, and now to a southern-Appalachian geologist. She was born on Coney Island and grew up in a tenement in Williamsburg Brooklyn. There was not a little Flatbush in her manner, soul, and speech. Her father was Russian, and his name in the old country was Herschel Litvak. In Brooklyn, he called himself Harry Fishman, and sometimes Harry Block. According to his daughter, English names meant nothing to Russian Jews in Brooklyn. She grew up Fishman and became in marriage Epstein and Harris, signing her geology with her various names and imparting some difficulty to followers of her professional papers. With her permission, I will call her Anita, and let the rest of the baggage go. Straightforwardly, as a student, she went into geology because geology was a means of escaping the ghetto. “I knew that if I went into geology I would never have to live in New York City,” she once said to me. “It was a way to get out.” She was nineteen years old when she was graduated from Brooklyn College. She remembers how pleased and astounded she was to learn that she could be paid “for walking around in mountains.” Paid now by the United States Geological Survey, she has walked uncounted mountains.
After the level farmlands of northwestern Ohio, the interstate climbed into surprising terrain—surprising enough to cause Anita to suspend her attack on plate tectonics. Hills appeared. They were steep in pitch. The country resembled New England, a confused and thus beautiful topography of forested ridges and natural lakes, stone fences, bunkers and bogs, cobbles and boulders under maples and oaks: Indiana. Rough and semi-mountainous, this corner of Indiana was giving the hummocky lie to the reputed flatness of the Middle West. Set firmly on the craton—the Stable Interior Craton, unstirring core of the continent—the whole of Middle America is structurally becalmed. Its basement is coated with layers of rock that are virtually flat and have never experienced folding, let alone upheaval. All the more exotic, then, were these abrupt disordered hills. Evidently superimposed, they almost seemed to have been created by the state legislature to relieve Indiana. Not until the nineteenth century did people figure out whence such terrain had come, and how and why. “Look close at those boulders and you’ll see a lot of strangers,” Anita remarked. “Red jasper conglomerates. Granite gneiss. Basalt. None of those are from anywhere near here. They’re Canadian. They have been transported hundreds of miles.”
The ice sheets of the present era, in their successive spreadings overland, have borne immense freight—rock they pluck up, shear off, rip from the country as they move. They grind much of it into gravel, sand, silt, and clay. When the ice melts, it gives up its cargo, dumping it by the trillions of tons. The most recent advance has been called the Wisconsinan ice sheet, because its effects are well displayed in Wisconsin. Its effects, for all that, are not unimpressive in New York. The glacier dumped Long Island where it is (nearly a hundred per cent of Long Island), and Nantucket, and Cape Cod, and all but the west end of Martha’s Vineyard. Wherever the ice stopped and began to melt back, it signed its retreat with terminal moraines—huge accumulations of undifferentiated rock, sand, gravel, and clay. The ice stopped at Perth Amboy, Metuchen, North Plainfield, Madison, Morristown—leaving a sinuous, morainal, lobate line that not only connects these New Jersey towns but kee
ps on going to the Rocky Mountains. West of Morristown, old crystalline rock from the earth’s basement—long ago compressed, distorted, and partially melted, driven upward and westward in the Appalachian upheavals—stands now in successive ridges, which are called the New Jersey Highlands. They trend northeast-southwest. With a notable exception, they have discouraged east-west construction of roads. When the last ice sheet set down its terminal moraine, it built causeways from one ridge to another, on which Interstate 80 rides west. Over the continent, the ice had spread southward about as evenly as spilled milk, and there is great irregularity in its line of maximum advance. South of Buffalo, it failed to reach Pennsylvania, but it plunged deep into Ohio, Indiana, Illinois. The ice sheets set up and started Niagara Falls. They moved the Ohio River. They dug the Great Lakes. The ice melted back in stages. Pausing here and there in temporary equilibrium, it sometimes readvanced before continuing its retreat to the north. Wherever these pauses occurred, as in northeastern Indiana, boulders and cobbles and sand and gravel piled up in prodigal quantity—a cadence of recessional moraines, hills of rock debris. The material, heterogeneous and unsorted, has its own style of fabric, in which geologists can see the moves and hesitations of the ice, not to mention its weight and velocity. Scottish farmers, long before they had any idea what had laid such material upon Scotland, called it till, by which they meant to convey a sense of “ungenial subsoil,” of coarse obdurate land.
“This would be a good place for a golf course,” Anita remarked, and scarcely had she uttered the words than—after driving two thousand yards on down the road with a dogleg to the left—we were running parallel to the fairways of a clonic Gleneagles, a duplicated Dumfries, a faxed Blairgowrie, four thousand miles from Dumfriesshire and Perthshire, but with natural bunkers and traps of glacial sand, with hummocky roughs and undulating fairways, with kettle depressions, kettle lakes, and other chaotic hazards. “If you want a golf course, go to a glacier” is the message according to Anita Harris. “Golf was invented on the moraines, the eskers, the pitted outwash plains—the glacial topography—of Scotland,” she explained. “All over the world, when people make golf courses they are copying glacial landscapes. They are trying to make countryside that looks like this. I’ve seen bulldozers copying Scottish moraines in places like Louisiana. It’s laughable.”
On warm afternoons in summer, the meltwater rivers that pour from modern glaciers become ferocious and unfordable, like the Suiattle, in Washington, coming down from Glacier Peak, like the Yentna, in Alaska, falling in tumult from the McKinley massif. Off the big ice sheets of the Pleistocene have come many hundreds of Suiattles and Yentnas, most of which are gone now, leaving their works behind. The rivers have built outwash plains beyond the glacial fronts, sorting and smoothing miscellaneous sizes of rock—moving cobbles farther than boulders, and gravels farther than cobbles, and sands farther than gravels, and silt grains farther than sands—then gradually losing power, and filling up interstices with groutings of clay. Enormous chunks of ice frequently broke off the retreating glaciers and were left behind. The rivers built around them containments of gravel and clay. Like big, buried Easter eggs, the ice sat there and slowly melted. When it was gone, depressions were left in the ground, pitting the outwash plains. The depressions have the shapes of kettles, or at least have been so described, and “kettle” is a term in geology. All kettles contained water for a time, and some contain water still. Rivers that developed under glaciers ran in sinuous grooves. Rocks and boulders coming out of the ice fell into the rivers, building thick beds contained between walls of ice. When the glacier was gone, the riverbeds were left as winding hills. The early Irish called them eskers, meaning pathways, because they used them as means of travel above detentive bogs. Where debris had been concentrated in glacial crevasses, melting ice left hillocks, monticles, hummocks, knolls, braes—collections of lumpy hills known generically to the Scots as kames. In Indiana as in Scotland—in La Bresse and Estonia as in New England and Quebec—the sort of country left behind after all these features have been created is known as kame-and-kettle topography.
The interstate was waltzing with the glacier—now on the out-wash plain, now on moraine, among the kettles and kames of Scottish Indiana. Roadcuts were green with vetch covering glacial till. We left 80 for a time, the closer to inspect the rough country. The glacier had been away from Indiana some twelve thousand years. There were many beds of dried-up lakes, filled with forest. In the Boundary Waters Area of northern Minnesota, the ice went back ten thousand years ago, possibly less, and most of the lakes it left behind are still there. The Boundary Waters Area is the scene of a contemporary conservation battle over the use and fate of the lakes. “Another five thousand years and there won’t be much to fight about,” Anita said, with a shrug and a smile. “Most of those Minnesota lakes will probably be as dry as these in Indiana.” Some of the larger and deeper ones endure. We made our way around the shores of Lake James, Bingham Lake, Lake of the Woods, Loon Lake. Like Walden Pond, in Massachusetts, they were kettles.
The woods around them were bestrewn with boulders, each an alien, a few quite large. If a boulder rests above bedrock of another type, it has obviously been carried some distance and is known as an erratic. In Alaska, I have come upon glacial erratics as big as office buildings, with soil developing on their tops and trees growing out of them like hair. In Pokagon State Park, Indiana, handsome buildings looked out on Lake James—fieldstone structures, red and gray, made of Canadian rocks. The red jasper conglomerates were from the north shore of Lake Huron. The banded gray gneisses were from central Ontario. The sources of smaller items brought to Indiana by the ice sheets have been less easy to trace—for example, diamonds and gold. During the Great Depression, one way to survive in Indiana was to become a pick-and-shovel miner and earn as much as five dollars a day panning gold from glacial drift—as all glacial deposits, sorted and unsorted, are collectively called. There were no nuggets, nothing much heavier than a quarter of an ounce. But the drift could be fairly rich in fine gold. It had been scattered forth from virtually untraceable sources in eastern Canada. One of the oddities of the modern episodes of glaciation is that while three-fifths of all the ice in the world covered North America and extended south of Springfield, Illinois, the valley of the Yukon River in and near Alaska was never glaciated, and as a result the gold in the Yukon drainage—the gold of the richest placer streams ever discovered in the world—was left where it lay, and was not plucked up and similarly scattered by overriding ice. Miners in Indiana learned to look in their pans for menaccanite—beanlike pebbles of iron and titanium that signalled with some consistency the propinquity of gold. The menaccanite had come out of the exposed Precambrian core of Canada—the Canadian craton, also known as the Canadian Shield. There were garnets in the gold pans, too—and magnetite, amphibole, corundum, jasper, kyanite. Nothing in that list is native to Indiana, and all are in the Canadian Shield. There is Canadian copper in the drift of Indiana, and there are diamonds that are evidently Canadian, too. Hundreds have been discovered—pink almond-shaped hexoctahedrons, blue rhombic dodecahedrons. Weights have approached five carats, and while that is modest compared with twenty-carat diamonds found in Wisconsin, these Indiana diamonds have nonetheless been accorded the stature of individual appellations: the Young Diamond (1898), the Stanley Diamond (1900).
The source of a diamond is a kimberlite pipe, a form of diatreme—a relatively small hole bored through the crust of the earth by an expanding combination of carbon dioxide and water which rises from within the earth’s mantle and moves so fast driving magma to the surface that it breaks into the atmosphere at supersonic speeds. Such events have occurred at random through the history of the earth, and a kimberlite pipe could explode in any number of places next year. Rising so rapidly and from so deep a source, a kimberlite pipe brings up exotic materials the like of which could never appear in the shallow slow explosion of a Mt. St. Helens or the flows of Kilauea. Among the materials are dia
monds. Evidently, there are no diamond pipes, as they are also called, in or near Indiana. Like the huge red jasper boulders and the tiny flecks of gold, Indiana’s diamonds are glacial erratics. They were transported from Canada, and by reading the fabric of the till and taking bearings from striations and grooves in the underlying rock—and by noting the compass orientation of drumlin hills, which look like sculptured whales and face in the direction from which their maker came—anybody can plainly see that the direction from which the ice arrived in this region was something extremely close to 045°, northeast. At least one pipe containing gem diamonds must exist somewhere near a line between Indianapolis and the Otish Mountains of Quebec, because the ice that covered Indiana did not come from Kimberley—it formed and grew and, like an opening flower, spread out from the Otish Mountains. With rock it carried and on rock it traversed, it narrated its own journey, but it did not reveal where it got the diamonds.
There is a layer in the mantle, averaging about sixty miles below the earth’s surface, through which seismic tremors pass slowly. The softer the rock, the slower the tremor—so it is inferred that the low-velocity zone, as it is called, is close to its melting point. In the otherwise rigid mantle, it is a level of lubricity upon which the plates of the earth can slide, interacting at their borders to produce the effects known as plate tectonics. The so-termed lithospheric plates, in other words, consist of crust and uppermost mantle and can be as much as ninety miles thick. Diamond pipes are believed to originate a good deal deeper than that—and in a manner which, as most geologists would put it, “is not well understood.” After drawing fuel from surrounding mantle rock—compressed water from mica, in all likelihood, and carbon dioxide from other minerals—the material is thought to work slowly upward into the overlying plate. Slow it may be at the start, but a hundred and twenty miles later it comes out of the ground at Mach 2. The result is a modest crater, like a bullet hole between the eyes.
