Bill Bryson - A Walk In The Woods

The continents didn’t just move in and out from each other in some kind of grand slow-motion square dance but spun in lazy circles, changed their orientation, went on cruises to the tropics and poles, made friends with smaller landmasses and brought them home. Florida once belonged to Africa. A corner of Staten Island is, geologically, part of Europe. The seaboard from New England up to Canada appears to have originated in Morocco. Parts of Greenland, Ireland, Scotland, and Scandinavia have the same rocks as the eastern United States-are, in effect, ruptured outposts of the Appalachians. There are even suggestions that mountains as far south as the Shackleton Range in Antarctica may be fragments of the Appalachian family.

The Appalachians were formed in three long phases (or orogenies, as geologists like to call them) known as the Taconic, Acadian, and Alleghenian. The first two were essentially responsible for the northern Appalachians, the third for the central and southern Appalachians. As the continents bumped and nudged, sometimes one continental plate would slide over another, pushing ocean floor before it, reworking the landscape for 150 miles or more inland. At other times it would plunge beneath, stirring up the mantle and resulting in long spells of volcanic activity and earthquakes. Sometimes the collisions would interleave layers of rock like shuffled playing cards.

It is tempting to think of this as some kind of giant continentsized car crash, but of course it happened with imperceptible slowness. The proto-Atlantic Ocean (sometimes more romantically called Iapetus), which filled the void between continents during one of the early splits, looks in most textbook illustrations like a transitory puddle-there in Fig. 9A, vanished in Fig. 9B, as if the sun had come out for a day or so and dried it up-yet it existed far longer, hundreds of millions of years longer, than our own Atlantic has. So it was with the formation of mountains. If you were to travel back to one of the mountain-building phases of the Appalachians, you wouldn’t be aware of anything geologically grand going on, any more than we are sensible now that India is plowing into Asia like a runaway truck into a snowbank, pushing the Himalayas up by a millimeter or so a year.

And as soon as the mountains were built, they began, just as ineluctably, to wear away. For all their seeming permanence, mountains are exceedingly transitory features. In Meditations at 10,000 Feet, writer and geologist James Trefil calculates that a typical mountain stream will carry away about 1,000 cubic feet of mountain in a year, mostly in the form of sand granules and other suspended particles. That is equivalent to the capacity of an average-sized dump truck-clearly not much at all. Imagine a dump truck arriving once each year at the base of a mountain, filling up with a single load, and driving off, not to reappear for another twelve months. At such a rate it seems impossible that it could ever cart away a mountain, but in fact given sufficient time that is precisely what would happen. Assuming a mountain 5,000 feet high with 500,000 million cubic feet of mass-roughly the size of Mount Washington-a single stream would level it in about 500 million years.

Of course most mountains have several streams and moreover are exposed to a vast range of other reductive factors, from the infinitesimal acidic secretions of lichen (tiny but relentless!) to the grinding scrape of ice sheets, so most mountains vanish very much more quickly-in a couple of hundred million years, say. Right now the Appalachians are shrinking on average by 0.03 millimeters per year. They have gone through this cycle at least twice, possibly more-rising to awesome heights, eroding away to nothingness, rising again, each time recycling their component materials in a dazzlingly confused and complex geology.

The detail of all this is theory, you understand. Very little of it is more than generally agreed upon. Some scientists believe the Appalachians experienced a fourth, earlier mountain-building episode, called the Grenville Orogeny, and that there may have been others earlier still. Likewise, Pangaea may have split and reformed not three times but a dozen times, or perhaps a score of times. On top of all this, there are a number of lapses in the theory, chief of which is that there is little direct evidence of continental collisions, which is odd, even inexplicable, if you accept that at least three continents rubbed together with enormous force for a period of at least 150 million years. There ought to be a suture, a layer of scar tissue, stretching up the eastern seaboard of the United States. There isn’t.

I am no geologist. Show me an unusual piece of greywacke or a handsome chunk of gabbro and I will regard it with respect and listen politely to what you have to say, but it won’t actually mean anything to me. If you tell me that once it was seafloor ooze and that through some incredible sustained process it was thrust deep into the earth, baked and squeezed for millions of years, then popped back to the surface, which is what accounts for its magnificent striations, its shiny vitreous crystals, and flaky biotate mica, I will say, “Goodness!” and “Is that a fact!” but I can’t pretend that anything actual will be going on behind my game expression.

Just occasionally am I permitted an appreciative glimpse into the wonder that is geology, and such a place is the Delaware Water Gap. There, above the serene Delaware River, stands Kittatinny Mountain, a wall of rock 1,300 feet high, consisting of resistant quartzite (or so it says here) that was exposed when the river cut a passage through softer rock on its quiet, steady progress to the sea. The result in effect is a cross-section of mountain, which is not a view you get every day, or indeed anywhere else along the Appalachian Trail that I am aware of. And here it is particularly impressive because the exposed quartzite is arrayed in long, wavery bands that lie at such an improbably canted angle-about 45 degrees-as to suggest to even the dullest imagination that something very big, geologically speaking, happened here.

It is a very fine view. A century or so ago people compared it to the Rhine and even (a little ambitiously, I’m bound to say) the Alps. The artist George Innes came and made a famous painting called “Delaware Water Gap.” It shows the river rolling lazily between meadowy fields dotted with trees and farms, against a distant backdrop of sere hills, notched with a Vwhere the river passes through. It looks like a piece of Yorkshire or Cumbria transplanted to the American continent. In the 1850s, a plush 250room hotel called Kittatinny House rose on the banks of the river and was such a success that others soon followed. For a generation after the Civil War, the Delaware Water Gap was the place to be in summer. Then, as is always the way with these things, the White Mountains came into fashion, then Niagara Falls, then the Catskills, then the Disneys. Now almost no one comes to the Water Gap to stay. People still pass through in large numbers, but they park in a turnout, have a brief appreciative gaze, then get back in their cars and drive off.

Today, alas, you have to squint, and pretty hard at that, to get any notion of the tranquil beauty that attracted Innes. The Water Gap is not only the nearest thing to spectacle in eastern Pennsylvania but also the only usable breach in the Appalachians in the area of the Poconos. In consequence, its narrow shelf of land is packed with state and local roads, a railway line, and an interstate highway with a long, unimaginative concrete bridge carrying streams of humming trucks and cars between Pennsylvania and New Jersey-the whole suggesting, as McPhee neatly put it in In Suspect Terrain, “a convergence of tubes leading to a patient in intensive care.”