by John McPhee
In 1880, Robert Louis Stevenson—aged thirty, newly married, consumptive—fled the “poisonous fog” of San Francisco and went into the mountains above Calistoga, where he and his American bride and her twelve-year-old son spent the summer squatting in an empty cabin at a closed-down mine called Silverado. From their high bench among rusting machinery and rubbled tailings, they looked down into the green rectangles of the Napa Valley.
The floor of the valley is extremely level to the roots of the hills; only here and there a hillock, crowned with pines, rises like the barrow of some chieftain famed in war.
Stevenson had more than a passing sense of the geology.
Here, indeed, all is new, nature as well as towns. The very hills of California have an unfinished look; the rains and streams have not yet carved them to their perfect shape.
Hot Springs and White Sulphur Springs are the names of two stations on the Napa Valley railroad; and Calistoga itself seems to repose on a mere film above a boiling, subterranean lake.
He began making notes for what became “The Silverado Squatters” and various settings for later work. He described the summit of Mt. St. Helena as “a cairn of quartz and cinnabar.” He noted that Calistoga was a coined name. A Mormon promoter had been thinking of America’s premier spa. Fortunately, his idea failed to travel, or there would be a Nevastoga, a Utastoga, a Wyostoga. Rattlesnakes resounded in the air like crickets. For a couple of months, Stevenson didn’t know what he was hearing.
The rattle has a legendary credit; it is said to be awe-inspiring, and, once heard, to stamp itself forever in the memory. But the sound is not at all alarming; the hum of many insects, and the buzz of the wasp convince the ear of danger quite as readily. As a matter of fact, we lived for weeks in Silverado, coming and going, with rattles sprung on every side, and it never occurred to us to be afraid. I used to take sun-baths and do calisthenics in a certain pleasant nook among azalea and calcanthus, the rattles whizzing on every side like spinning-wheels, and the combined hiss or buzz rising louder and angrier at any sudden movement; but I was never in the least impressed, nor ever attacked. It was only towards the end of our stay that a man down at Calistoga, who was expatiating on the terrifying nature of the sound, gave me at last a very good imitation; and it burst on me at once that we dwelt in the very metropolis of deadly snakes, and that the rattle was simply the commonest noise in Silverado.
Without so much as a warning rattle, the owner of the Silverado Mine turned up one day, discovering and embarrassing the illegal squatter.
I somewhat quailed. I hastened to do him fealty, said I gathered he was the Squattee … .
Stevenson’s summer was four years after the battle of the Little Bighorn. The West was that Old. Yet he counted fifty vineyards in the Napa Valley. Farmers had been in the valley for nearly half a century. In the eighteen-thirties, George Yount, of North Carolina, had been converted to Catholicism and had had himself baptized Jorge Concepción Yount in order to obtain a Mexican land grant of almost twelve thousand acres. An English surgeon to whom the Mexicans also gave a Napa Valley land grant named his place Rancho Carne Humana. In 1876, the Beringer winery was founded by Germans from Mainz. In approximate replication of their ancestral home, they built Rhine House in 1883. The stretch limos park there now, beside wide lawns under tall elms. Off the jump seats come people who go inside and lay down forty dollars for the magnum opus Beringer: A Napa Valley Legend. Leafing through the book, Moores picks up the information that the foundation and first story of Rhine House are limestone. He goes outside and squints at the house through his ten-power Hastings Triplet. “Jesus Christ!” he says. For Moores, this is new ground. He has never before seen limestone that came out of a volcano. “It’s poorly welded volcanic ash with lots of big vesicles, pumice lapilli,” he goes on. “It’s friable volcanic ash! A welded tuff! An ignimbrite!”
Louis Martini’s cement-block roadhouse, south of St. Helena on the way to Rutherford, is a low, clean-lined, postroad-modern building that lacks windows and has a long portico and a few wrought-iron lamps. Its architectural statement is upper-middle prime rib. Among the building’s tiled rooms are showcases of Martini wines and a long dark bar. No one hurries anyone away, and in the cool quiet we sample half a dozen bottles, talking geology with our noses in the outcrop. Louis Martini’s wines are straightforward, stalwart, allusive, volcanic. They are prepared to travel—like the terrane they derive from, and like the first Martini (who emigrated from Italy in 1894), and, according to Moores, like Italy itself, which departed from Europe in the Jurassic but later went home. Italy became a prong of Africa, he says, cupping his hand and orbiting a cabernet sauvignon. Italy left Europe, joined Africa, and later smashed back into Europe in the collision that made the Alps. The quarried Tuscan serpentines in the walls of the Duomo and the Giotto campanile are particles of the ophiolites that underscore this story.
Martini’s pinot noir has the brawny overtones of an upland Rioja, the resilient spring of an athletic Medoc. Moores wonders if I have noticed that “the claret coast of France” and the Cantabrian coast of northern Spain seem to suggest an open bivalve, with Bordeaux at the hinge. In the early Cretaceous, when the Atlantic was young and narrow, there was no water between western France and northern Spain; the hinge was closed. The whole of Iberia got caught up in the spreading, and was perhaps yanked by Africa as Africa moved northeast. A rift opened, and widened, and became the Bay of Biscay. In a comparatively short time, the Iberian Peninsula swung ninety degrees and assumed its present position.
During the zinfandel, Moores summarizes the United Kingdom as “the remnants of a collision that occurred at the end of the Silurian.” Melanges resembling the Franciscan were caught in it, he says—for example, Caernarvonshire and Anglesey, in Wales. Collisional ranges appeared, later to be dismembered by the opening of the ocean. In France, the Massif Central is actually a continuation of the northern Appalachians. The southern Appalachians go up to New Jersey and then jump to North Africa as the Atlas Mountains and then to the Iberian Plateau and to the Pyrenees, which were later enhanced by compressions that developed as Spain swung around.
During the Napa Valley Reserve Petite Sirah, I mention the Brooks Range, where I have recently been.
The Brooks Range, Moores says, is a sliver of exotic continental material that came in from above Alaska, hit a subduction zone, and put ophiolite sequences along what is now the south slope. In the collision that followed, the exotic sliver was folded into mountains.
“When was that?”
“I forget. In the Jurassic, probably, or the early Cretaceous.”
The Seward Peninsula—where Nome is, in west-central Alaska—is a piece of Jurassic blue schist surrounded by ophiolitic rock, but no one knows where the Seward Peninsula came from. For that matter, he adds, there is no certainty about where any of Alaska came from. It seems to consist entirely of exotic pieces that drifted to North America in Mesozoic time. South of the Denali Fault, which runs east-west and is close to Mt. McKinley, is the huge terrane that geologists call Wrangellia. It was an island arc, developed over an ocean plateau. Moores describes Mt. McKinley as “a bit of granite” that came up into Wrangellia after it arrived. Not long ago, Japan was attached to Asia. It drifted away. Japan is coming toward North America one centimetre a year. It may be a part of Alaska in eight hundred million years.
There is a shift change at Louis Martini’s. One hostess replaces another. The new one says to her departing colleague, “Be careful out there. It’s intense. They’re driving all over the road.”
That conversation in Louis Martini’s winery occurred in 1978, when the theory of plate tectonics was ten years old and people who talked the way Moores was talking were widely considered daft. I may have thought it was the wine, but I was not in a position to know. Over the years, Moores and I have returned so often to the subject of world ophiolites and global tectonics—as they have recorded and described the changing face of the planet—that what follows i
s a sampling of all such dialogues, which I have compiled in the hope of reflecting, through his remarks, some of the geologic thinking of the nineteen-seventies, eighties, and nineties.
In order to move from place to place and let time float free, it would be well to bear in mind that the plate-tectonics narrative of the past fifteen hundred million years principally describes the assembling and disassembling of two supercontinents—Rodinia and Pangaea. Of the mountain ranges of Rodinia we have nothing today but evidential roots, attended by some ophiolites that speak of the collisions that built those Precambrian mountains. After Rodinia breaks up, about six hundred million years ago, its fragments result in a map of the world so different from the present one that it could be a map of a different planet; Kazakhstan, for example, is contiguous with Norway and New England. By two hundred and fifty million years before the present, the scattered continents and microcontinents have reassembled as Pangaea, whose sutures are today expressed in dwindled but palpable topographic relief (the Urals, the Appalachians). While Pangaea in turn disassembles, in the Mesozoic, not only is the Atlantic Ocean born but all over the world recognizable pieces of dispersing land move in the direction of the present map.
Wherever tectonically emplaced ophiolites happen to be, they lead to local geographic histories within the general story of the successive supercontinents. The presence of an ophiolite is a notation that while something is added to a continental margin an ocean basin of unknown size disappears. It could be Pacific-size. Moores is planning a book relating ophiolites to their origins. Chapter 1 might develop his analogy between the great complexity of islands north of modern Australia and the loose landmasses that once cluttered the Farallon Ocean off western North America and are now consolidated as California and other additions to the continent. North of modern Australia is a confused piece of the globe, made so by the encroaching motions of the Indo-Australian, Eurasian, and Pacific plates. They have broken the crust between them into microplates that look like the results of severe impact on a hard-boiled egg. The small pieces continue to be rigid, and remain in place, but the shell is shattered. The Philippine Plate, largest of the microplates, is surrounded by ocean trenches six and seven miles deep. On the east, Pacific crust is going under the Philippine Plate. On the west, Asian crust is going into the Manila Trench, where melting has produced the West Luzon arc and where Taiwan is docking with mainland China. That much is straightforward compared with the many smaller microcontinents and minor ocean basins that are also in the region, where a subduction zone is apparently in the process of flipping over, another is bending back upon itself, and another has curled around almost far enough to meet itself in a circle. This is a carnival of plate tectonics—of numerous island-arc-to-island-arc collisions and continent-to-island-arc collisions. As in the story of western North America, some arcs seem to be joining one another before attaching to a continent.
Ocean crust of the Indo-Australian Plate descending into the Java Trench has resulted in the arc from the Andaman Islands to the Banda Sea: Sumatra, Java, Bali, others. Where the Australian continental shelf has already jammed the trench and has picked up the Papuan ophiolites, it has buckled its own Australian sediments sixteen thousand feet into the air, making most of New Guinea. Moores thinks that the subduction zone will flip over now, and the Pacific Plate will begin to slide under Australia. In that event, he says, “Australia will keep going and will pick up the Philippines and every intervening island and then go after Japan on Japan’s way east.”
“You’re saying that a north-dipping subduction zone will swing like a pendulum and become a south-dipping subduction zone? That is possible?”
“That seems to be what’s happening. That’s what you see in the seismicity. There’s nothing magical or indelible about the present plate margins. Consuming margins, especially, can change their nature very readily.”
In the Sierra Nevada near the Mother Lode, where the geology suggests to plate theorists that a pair of ocean trenches came together in the Jurassic, evidently there was no spreading center, and the trenches just ate up the crust between them, leaving undigested the accretionary phyllites, cherts, argillites, and limestones that lie uphill from Auburn. To many people, the idea of unspreading seafloor being consumed from two sides by converging trenches has seemed especially farfetched. In the late nineteen-seventies, however, a pair of active trenches doing exactly that was discovered in the Celebes Sea. They are moving toward each other. The intervening crust is disappearing. With depth finders and seismographs, geologists can see this happening, but they can’t explain it.
Tracing a finger northward on a geologic map of the world, Moores follows ophiolites from Beijing to Siberia. There are several parallel strings of them, connecting two Precambrian continental blocks. The place-names on his map are written in Cyrillic characters, because it is a Russian map, but the rocks are readable, in the international colors and symbols of the science. “These sutures tell you that China used to be separated from Siberia by two or three oceans,” Moores says. “They disappeared in the Paleozoic.”
North of China, the Verkhoyanski Mountains make a sinuous track through Siberia to the Arctic Laptev Sea. Landmasses extend two thousand miles east of the Verkhoyanskis and four thousand west, yet the mountains contain rocks derived from a spreading center in a vanished ocean. The Verkhoyanski ophiolites are early Cretaceous in age—at least a hundred million years younger than the sutures in China, which were involved in Pangaea’s assembling. The Verkhoyanski collision occurred after the supercontinent started to break up. As the Atlantic Ocean widened and the North American Plate moved west and the Eurasian Plate moved east, the two landmasses eventually touched each other, nearly halfway around the world, and made the Verkhoyanski Mountains. This was the plate boundary where Asia and North America actually came together. The Chukchi Sea and the Bering Sea, which separate Alaska and Siberia, are merely water lying on the North American continent.
Moores moves west to the Urals, which are flanked with ophiolites emplaced in Silurian time, in the middle Paleozoic, at the edge of the ocean that separated Asia from Europe. The ensuing collision did not begin until the Mississippian period, a hundred million years later. The fact that so much time passed between the emplacement of the ophiolites and the continent-to-continent collision means that a lot of seafloor was consumed, at least enough for an ocean a thousand miles wide. Russian geologists call this the Paleoasian Ocean. When the collision finally came, it completed Pangaea, two hundred and fifty million years ago.
Putting my hand on Spitsbergen and the rest of the Svalbard archipelago—ten degrees from the North Pole—I ask him, “What are they?”
With a sweeping move down the Atlantic he connects their story to Alabama. Among the various ocean basins that disappeared while Pangaea coalesced, the most intensively studied is the one that geologists have named for Iapetus, the father of Atlas: the ocean basin—or group of ocean basins—that lay between continental landmasses that are now substantial parts of Europe, Africa, and North America. Iapetus appears to have been larger than the modern Atlantic. Five hundred million, four hundred million, and three hundred million years ago, as Iapetus gradually closed, the lands on either side in no way resembled the modern configurations of Europe and North America, but they were composed of rock we see in those places now. In the Iapetus Ocean, or oceans, were arcs and trenches, spreading centers, microplates, subduction zones, strike-slip faults, a mess of islands. Much of this seems to have resembled the Farallon Ocean off California in Mesozoic time, and the southwest Pacific today. The collisions that eradicated Iapetus and made a kind of headcheese of the intervening islands began more or less at Spitsbergen, and—roughly, sporadically—crunched their way south. In the terms of the Old Geology, this was the series of mountain-making episodes that were known as the Caledonian, Taconic, Acadian, and Alleghenian orogenies. The trail of these events was blazed with ophiolites. Ophiolitic emplacements in Newfoundland, Quebec, and Vermont, for exam
ple, signal the docking of an island arc—the event long known as the Taconic Orogeny. The consequential mountain building in New England and much of eastern Canada was thought—in the early days of plate tectonics—to be the result of a continent-to-continent collision. “The Taconic Orogeny is a collision of ophiolitic terrane with the North American continent, full stop,” Moores says. “It is an oceanic terrane—and not yet Europe—colliding with North America.” In the assembling of New England, at least two more arcs followed. These Paleozoic additions to the eastern seaboard are remarkably analogous to the assembling of California an era later.