Basin and Range
The Earth Generated and Anatomized
I read Basin and Range, John McPhee’s celebration of geology, during a long plane ride from Portland to Boston. I am not a morning person, but I managed to reach the airport long before the flight (and almost before dawn) to secure a “geologist’s seat”—by the window, before the wing and on the left side—all for a view of Mt. St. Helens. I was not disappointed.
Volcanoes, with their symmetry and gently parabolic slopes, are perhaps the most stunning objects of a world dominated by irregular topography. If volcanoes tower above the local landscape—as they do in the northwestern United States—the effect is even more striking. When I flew by in early March, the snow had melted at lower elevations, leaving all the surrounding hills brown. But three gleaming white volcanic peaks stood out above them—Mt. St. Helens, with its cloud of steam still rising a thousand feet into the air, Mt. Adams beside it, and the granddaddy of the Cascade volcanoes, Mt. Rainier, behind. It was the most awesome sight I have ever seen from an airplane window.
We have been poor at assimilating the great lessons that geology teaches—the earth’s ceaseless motion and immensity of time (or “deep time” as McPhee calls it), I well remember the catechism I learned in grade school: Mt. Lassen, which erupted in 1914, is the only active volcano in the United States (Alaska and Hawaii were still colonial possessions at the time). Written history recorded no eruptions, so we declared that the internal fires had been quenched irrevocably. Lassen is but one peak in the Cascade chain; St. Helens is another. Every one of those volcanoes is potentially active—Shasta, Hood, Rainier, all of them. Mt. Rainier may bury Seattle before another earthquake levels San Francisco.
Geology presents its irreducible beauty in raw appearances—and who would gainsay it. But another, perhaps deeper, beauty lies in understanding. The Cascade volcanoes extend for hundreds of miles in a linear belt. Why are they so aligned? And why do they stop in northern California? Why do volcanoes tend to come in linear arrays anyway? Until the theory of “plate tectonics” revolutionized geology by constructing a new earth, these questions had no adequate answers. But now we recognize that dense oceanic rock is pushed downward (subducted) beneath lighter continental rock when two “plates”—the large, thin “wafers” that form the earth’s upper layer—push into each other, one with oceanic rock and the other with continental rock at its margin. As oceanic rock slides into the earth below a continent, friction induces partial melting of the sinking plate and, perhaps, some of the surrounding mantle rock as well. This molten material may rise to form a chain of volcanoes on the earth’s surface right above the sinking edge of the oceanic plate.
California struck (and either consumed or removed) a ridge on the ocean floor many millions of years ago. Hence, from San Francisco to the south, oceanic rock is no longer spreading into and under America; in fact the Pacific is largely moving north along the San Andreas Fault. But a shortened ridge persists in the eastern Pacific north of San Francisco, and the oceanic rock on its eastern flank is still spreading under America, where some of it melts and rises to form the Cascade volcanoes. When I viewed the lineup—Rainier, St. Helens, and, looking out the opposite window, Mt. Hood—I could almost see the old floor of the Pacific Ocean a hundred miles below me, and I apprehended those majestic volcanoes as mere pimples, minor vents for a restless earth.
John McPhee has captured this duality—beauty in particulars and satisfaction in general understanding—in his superb, highly personal book of reflections. He recognized that plate tectonics had revolutionized geology during the last two decades and he wanted to understand how the profession (and its earth) differed from the one he studied in a college course taken before the great instauration. He knew that he could not obtain the information he sought from didactic sermons in text-books or from interviews with leading figures in academic offices. He had to go into the field with geologists, and spend months observing daily scientific life, to grasp how a scientific revolution permeates the core of practice. For God does dwell in the details, and visceral comprehension can only arise from an immersion in particulars. As a scientist, I thank McPhee for understanding this, as so few who write about us do.
Before plate tectonics, there was no discernible God at all; only the details. Traditional introductory geology courses were catalogues of names for time slots, rocks, and landscapes, and they deserved the name that generations of undergraduates bestowed upon them—rocks for jocks. Both McPhee and I started with a course like that. He gives his list of fondly remembered terms; I could supply mine. My favorite was “paternoster lakes”—the chains of connected pools that often form near the edges of glaciers and once reminded someone of beads on a rosary, hence “ourfather” lakes. The terms did provide an interesting name for my friend’s pet rabbit—Inselberg Bornhardt. Beyond that I could never see much use for them. In the hands of a poet with good slides, such a course could be inspiring; usually it was insufferably dull. No matter though; it cannot be taught anymore. (And thank goodness for that; for I am not a poet, and I now teach the successor to rocks for jocks at Harvard.)
Plate tectonics has given us a unified theory for the behavior and history of the earth as a whole. It has coordinated and brought under a single rubric such disparate phenomena as: the reason for Iceland and Hawaii, the coincidence of earthquakes and volcanoes with ridges and subduction zones, the youth of the sea floor and the greater age of continental cores, and the great Permian extinction that wiped out up to 90 percent of marine invertebrates some 225 million years ago. (Iceland and Hawaii sit above vents for molten rock rising from the earth’s interior. Ridges and subduction zones mark lines of activity where plates meet, spread apart, collide, and rub against each other. New sea floor forms at ridges, spreads out, and disappears into subduction zones on a cycle measured in tens of millions of years, while continents stand high on their plates and cannot be subducted. The great extinction coincides with the fusion of all continents into a single Pangaea.) These phenomena, and hundreds of others, are no longer isolated facts. We can now present the earth as an integrated unit. Our science—and our courses—have become exciting; geology has regained a prestige it has not enjoyed since we discovered deep time and discernible history in the early nineteenth century, and Europe’s finest scientists became geologists.
As McPhee’s book opens, he is, of all places, on the George Washington Bridge. It makes sense. The Atlantic Ocean has had an off-again-on-again history during the last half billion years. It existed at the dawn of modern life in the great Cambrian explosion nearly 600 million years ago. But it closed gradually during the next 350 million years and disappeared entirely when New York collided with Europe at the end of the Permian. But it opened again soon thereafter and, beginning as a puddle, and then a channelway, grew as the sea floor spread beneath it at the mid-Atlantic Ridge. Our modern continents carry some curious scars of the collision; for the breakup of Pangaea did not occur precisely along the lines of previous suturing. Bits of ancient Europe remain stuck to the extreme eastern border of North America (as we know from the strictly European fossils found in their rocks), while smidgens of old America grace the western coasts of Norway and Scotland.
Much of New Jersey’s geology records the stretching and splitting that reformed the Atlantic. But New Jersey is a fossil; the action is now more than a thousand miles east at the mid-Atlantic Ridge. McPhee wanted to see plate tectonics at work, so he headed west with his mentor Ken Deffeyes, professor of geology at Princeton, to the Basin and Range province of Nevada.
The Basin and Range is a vast expanse of alternating parallel chains: hills and valley, hills and valley. This topography is the superficial expression of a pulling apart of the earth beneath. The earth’s crust is being stretched in Nevada. In response, it has fractured in a series of faults running perpendicular (north-south) to the direction of stretching (east-west). At each fault, the rocks on one side fall while those on the other rise, producing an alternating series of hills and valleys.
The Cascade volcanoes exist because the East Pacific spreading zone still operates north of San Francisco. But, as I mentioned before, California overrode the same zone farther south, as the North American plate moved west, pushed by sea floor forming at the mid-Atlantic Ridge more than 4,000 miles to the east. Many theories have been advanced to explain the Basin and Range province in terms of plate tectonics, but all involve the fate of this overridden Pacific spreading zone. In one version, the entire zone was subducted beneath California and still operates under the Basin and Range, uplifting Nevada and tearing it apart. In any case, the Basin and Range topography records the early history of a potential ocean. It may be a living reminder of eastern North America’s visage just before the Atlantic puddle reappeared some 200 million years ago. McPhee went to the Basin and Range to see plate tectonics in action, and his title is a symbol of our reconstructed, restless earth.
Basin and Range is a series of disparate but organically connected chapters recording McPhee’s personal journey. Some are loosely sequential, as McPhee travels with geologists from the fossilized fracture zones of New Jersey to the active topography of Nevada. Others explore the consequences of plate tectonics in different ways—by examining the practicalities in Deffeyes’s search for silver in abandoned mine tailings, and by contrasting plate tectonics with another great reconstruction of the earth presented by James Hutton in the late eighteenth century.
Where McPhee’s style works—and it usually does—he triumphs by succinet prose, by his uncanny ability to capture the essence of a complex issue, or an arcane trade secret, in a well-turned phrase. Consider his topographic characterization of the United States: “really a quartering of a continent, a drawer in North America. Pull it out and prairie dogs would spill off one side, alligators off the other….” Or his organic metaphor for “deep time”: “With your arms spread wide…to represent all time on earth, look at one hand with its line of life. The Cambrian begins in the wrist, and the Permian extinction is at the outer end of the palm. All of the Cenozoic is in a fingerprint, and in a single stroke with a medium-grained nail file you could eradicate human history.” If geology has two great themes—deep time and ceaseless motion—consider his one-liner for the second: “If by some fiat I had to restrict all this writing to one sentence, this is the one I would choose: The summit of Mt. Everest is marine limestone.”