by John McPhee
A braided river carries such an enormous burden of sand and gravel that it does not meander through its valley like most streams, making cutbanks to one side and point bars opposite. Instead, it runs in braided channels through its own broad bed. Looking at those Silurian conglomerates, I could all but hear the big braided rivers I had seen coming down from the Alaska Range, with gravels a mile wide, caribou and bears on the gravel, and channels flowing in silver plaits. If those rivers testify, as they do, to the erosional disassembling of raw young mountains, then so did the rock before us, with its clean river gravels preserved in river sand. “Geology repeats itself,” Anita said, and we moved along, touching, picking at the rock. She pointed out the horse-belly curves of channel-fill deposits, and the fact that none was deeper than five feet—a result of the braiding and the shifting of the channels. Evidently, the calm earth and quiet seas that were described by the older rock we had collected up the road had been utterly revolutionized in the event that built the ancient mountains, which, bald as the djebels of Arabia, had stood to the east and shed the sand and gravel this way. In the ripple marks, the crossbedding, the manner in which the sands had come to rest, Anita could see the westerly direction of the braided-river currents more than four hundred million years ago.
Three hundred years ago, William Penn arrived in this country and decided almost at once that the Lenape were Jews. “Their eye is little and black, not unlike a straight-look’t Jew,” he wrote home. “I am ready to believe them of the Jewish race … . A man would think himself in Dukes-place or Berry-street in London, when he seeth them.” They were “generally tall, straight, well-built” people “of singular proportion.” They greased themselves with clarified bear fat. Penn studied their language—the better to know them, the better to work out his treaties. “Their language is lofty, yet narrow, but like the Hebrew … . One word serveth in the place of three … . I must say that I know not a language spoken in Europe that hath words of more sweetness or greatness, in accent or emphasis, than theirs.” Penn heard “grandeur” in their tribal proper names. He listed them: Tammany, Poquessin, Rancocas, Shakamaxon. He could have added Wyomissing, Wissinoming, Wyoming. He made treaties with the Lenape under the elms of Shakamaxon. Tammany was present. He was to become the most renowned chief in the history of the tribe. Many years after his death, American whites in eastern cities formed societies in his name, and called him St. Tammany, the nation’s patron saint. Penn’s fondness for the Lenape was the product of his admiration. Getting along with the Lenape was not difficult. They were accommodating, intelligent, and peaceful. The Indians revered Penn as well. He kept his promises, paid his way, and was fair.
Under the elms of Shakamaxon, the pledge was made that Pennsylvania and the Lenape would be friends “as long as the sun will shine and the rivers flow with water.” Penn outlined his needs for land. It was agreed that he should have some country west of the Lenape River. The tracts were to be defined by the distance a man could walk in a prescribed time—typically one day, or two—at an easygoing pace, stopping for lunch, for the odd smoke, as was the Lenape manner. In camaraderie, the Penn party and the Indians gave it up somewhere in Bucks County. Penn went home to England. He died in 1718.
About fifteen years later, Penn’s son Thomas, a businessman who had a lawyer’s grasp of grasping, appeared from England with a copy of a deed he said his father had transacted, extending his lands to the north by a day and a half’s walk. He made it known to a new generation of Lenape, who had never heard of it, and demanded that they acquiesce in the completion of—as it came to be called—the Walking Purchase. With his brothers, John and Richard, he advertised for participants. He offered five hundred acres of land for the fleetest feet in Pennsylvania. In effect, he hired three marathon runners. When the day came—September 19, 1737—the Lenape complained. They could not keep up. But they followed. Their forebears had made a bargain. The white men “walked” sixtyfive miles, well into the Poconos. Even so blatant an affront might in time have been accepted by the compliant tribe. But now the brothers made an explosive mistake. Their new terrain logically required a northern boundary. Illogically, the one they drew did not run east to a point on the river close to the Water Gap but northeast on a vector that encompassed and annexed the Minisink. Massacres ensued. Buildings were burned. Up and down the river, white scalps were cut. The Lenape reached for “the French hatchet.” Peaceful, accommodating they once had been, but now they were participants in the French and Indian Wars. Where they had tolerated whites in the Minisink, they burned whole settlements and destroyed the occupants. They killed John Rush. They killed his wife, his son and daughter. They killed seventeen Vanakens and Vancamps. They pursued people on the river and killed them in their boats. They killed Hans Vanfleara and Lambert Brink, Piercewell Goulding and Matthew Rue. They could not, however, kill their way backward through time. They never would regain the Minisink.
As we moved along beside the screaming trucks, we were averaging about ten thousand years per step. The progression was not uniform, of course. There might be two million years in one fossil streambed, and then the next lamination in the rock would record a single season, or a single storm—on one flaky surface, a single drop of rain. We looked above our heads at the projecting underside of a layer of sandstone patterned with polygons, impressions made as the sand came pouring down in storm-flood waters over mud cracks that had baked in the sun. From a layer of conglomerate, Anita removed a pebble with the pick end of her rock hammer. “Milky quartz,” she said. “Bull quartz. We saw this rock back up the road in the Precambrian highlands. When the Taconic Orogeny came, it lifted the older rock, and erosion turned it into pebbles and sand, which is what is here in this conglomerate. It’s an example of how the whole Appalachian system continually fed upon itself. These are Precambrian pebbles, in Silurian rock. You’ll see Silurian pebbles in Devonian rock, Devonian pebbles in Mississippian rock. Geology repeats itself.” Now and again, we came to small numbers that had been painted long ago on the outcrops. Anita said she had painted the numbers when she and Jack Epstein were working on the geology of the Water Gap. She said, “I’d hate to tell you how many months I’ve spent here measuring every foot of rock.” Among the quartzites were occasional bands not only of sandstone but of shale. The shales were muds that had settled in a matter of days or hours and had filled in the lovely periodicity of the underlying ripples in the ancient river sand. For each picture before us in the rock, there was a corresponding picture in her mind: scenes of the early Silurian barren ground, scenes of the rivers miles wide, and, over all, a series of pictures of the big Taconic mountains to the east gradually losing their competition with erosion in the wash of Silurian rain—a general rounding down of things, with river gradients declining. There were pictures of subsiding country, pictures of rising seas. She found shale that had been the mud of an estuary, and fossil shellfish, fossil jellyfish, which had lived in the estuary. In thin dark flakes nearby she saw “a little black lagoon behind a beach.” And in a massive layer of clear white lithified sand she saw the beach. “You don’t see sand that light except in beaches,” she said. “That is beach sand. You would have looked westward over the sea.”
To travel then along the present route of Interstate 80, you would have been in need of a seaworthy shallow-draft boat. The journey could have started in mountain rapids, for the future site of the George Washington Bridge was under thousands of feet of rock. Down the huge fans of boulders and gravel that leaned against the mountains, the west-running rivers raced toward the epicontinental sea. They projected their alluvium into the water and spread it so extensively that up and down the long flanks of the Taconic sierra the alluvium coalesced, gradually building westward as an enormous collection of sediment—a deltaic complex. At the future site of the Water Gap, you would have shoved off the white beach and set a westerly course across the sea—looking back from time to time up the V-shaped creases of steep mountain valleys. That was the world in which t
he older rock of the Water Gap had been forming—the braided-river conglomerates, the estuary mud, the beach sand. In the Holocene epoch, the Andes would look like that, with immense fans of gravel coming off their eastern slopes—the essential difference being vegetation, of which there was virtually none in the early Silurian. The sea was shallow, with a sandy bottom, in Pennsylvania. The equator had shifted some and was running in the direction that is now northeast-southwest, through Minneapolis and Denver. There were muds of dark lime in the seafloors of Ohio, and from Indiana westward there were white-lime sands only a few feet under clear water.
If you had turned around and come back twenty-five million years later, in all likelihood you would still have been riding the sparkling waves of the limestone-platform sea, but its extent in the late Silurian is not well reported. Most of the rock is gone. There are widely scattered clues. Among the marine limestones that fell into the diamond pipe near Laramie, some are late Silurian in age. From Wyoming toward the east, there seems to have existed a vastly extrapolated sea. The extrapolation stops in Chicago. You would have come upon a huge coral reef, which is still there, which grew in Silurian time, and did not grow in a desert. It was a wave-washed atoll then, a Kwajalein, an Eniwetok, and in time it would become sugary blue dolomite packed with Silurian shells. After standing there more than four hundred million years, the dolomite would be quarried to become for many miles the concrete surface of Interstate 80 and to become as well the foundations of most of the tall buildings that now proclaim Chicago, as the atoll did in Silurian time. Interstate 80 actually crosses the atoll on bridges above the quarry, which is as close an approximation to the Grand Canyon as Chicago is likely to see, and may be its foremost attraction. Beyond the atoll, you would have come to other atolls and hypersaline seas. When water is about three times as salty as the ocean, gypsum will crystallize out. Sticking up from the bottom in central Ohio were dagger-length blades of gypsum crystal. You would have been bucking hot tropical trade winds then, blowing toward the equator, evaporating the knee-deep sea. East of Youngstown, red muds clouded the water—muds coming off the approaching shore. The beach was in central Pennsylvania now, near the future site of Bloomsburg, near the forks of the Susquehanna. The great sedimentary wedge of the delta complex had grown a hundred miles. The Taconic mountains were of humble size. The steep braided rivers were gone, their wild conglomerates buried under meandering mudbanked streams moving serenely through a low and quiet country—a rose-and-burgundy country. There were green plants in the red earth, for the first time ever.
Walking forward through time and past the tilted strata of the Water Gap, we had come to sandstones, siltstones, and shales, in various hues of burgundy and rose. In the irregular laminations of the rock—in its worm burrows, ripples, and crossbeds—Anita saw and described tidal channels, tidal flats, a river coming into an estuary, a barrier bar, a littoral sea. She saw the delta, spread out low and red, the Taconic mountains reduced to hills. We had left behind us the rough conglomerates and hard gray quartzites that had come off the Taconic mountains when they were high—the formation, known as Shawangunk, that forms the mural cliffs above the Delaware River. (The quartzites are paradisal to rappeling climbers, who refer in their vernacular to “the gap rap,” a choice part of “the Gunks.”) And now, half a mile up the highway and twenty million years up the time scale, we were looking at the younger of the two formations of which Kittatinny Mountain is locally composed. Generally red, the rock is named for Bloomsburg, outer reach of the deltaic plain in late Silurian time, four hundred and ten million years before the present.
Less than two hundred years before the present, when the United States was twenty-four years old, the first wagon road was achieved through the Water Gap. The dark narrow passage in rattlesnake-defended rock had seemed formidable to Colonial people, and the Water Gap had not served them as a transportational gateway but had been left aloof, mysterious, frightening, and natural.
In the hundred feet or so of transition rocks between the gray Shawangunk and the red Bloomsburg, we had seen the Silurian picture change from sea and seashore to a low alluviated coastal plain; and if we had a microscope, Anita said, we would see a few fish scales in the Bloomsburg river sands—from fish that looked like pancake spatulas, with eyes in the front corners.
In 1820, the Water Gap was discovered by tourists. They were Philadelphians with names like Binney.
Breaking away some red sandstone, Anita remarked that it was telling a story of cut-and-fill—the classic story of a meandering stream. The stream cuts on one side while it fills in on the other. Where bits and hunks of mudstone were included in the sandstone, the stream had cut into a bank so vigorously that it undermined the muddy soil above and caused it to fall. Meanwhile, from the opposite bank—from the inside of the bend in the river—a point bar had been building outward, protruding into the channel, and the point bar was preserved in clean sandstones, where curvilinear layers, the crossbeds, seemed to have been woven of rushes.
Confronted with a mountain sawed in half, a traveller would naturally speculate about how that might have happened—as had the Indians before, when they supposedly concluded that the Minisink had once been “a deep sea of water.” Samuel Preston agreed with the Indians. In 1828, in a letter to Hazard’s Register of Pennsylvania, Preston referred to the Water Gap as “the greatest natural curiosity in any part of the State.” He went on to hypothesize that “from the appearance of so much alluvial or made land above the mountain, there must, in some former period of the world, have been a great dam against the mountain that formed all the settlements called Minisink into a lake, which extended and backed the water at least fifty miles.” And therefore, he worked out, “from the water-made land, and distance that it appears to have backed over the falls in the river, the height must, on a moderate calculation, have been between one hundred and fifty and two hundred feet, which would have formed a cataract, in proportion to the quantity of water, similar to Niagara.” Preston was a tourist, not a geologist. The first volume of Charles Lyell’s Principles of Geology, the textbook that most adroitly explained the new science to people of the nineteenth century, would not be published for another two years, let alone cross the sea from London. All the more remarkable was Preston’s Hypothesis. Like many an accomplished geologist who would follow, Preston made excellent sense even if he was wrong. Withal, he had the courage of his geology. “If any persons think my hypothesis erroneous,” he concluded, “they may go and examine for themselves … . The Water Gap will not run away.”
While sediments accumulated slowly in the easygoing lowlands of the late Silurian world, iron in the rock was oxidized, and therefore the rock turned red. Alternatively, it could have been red in the first place, if it weathered from a red rock source. There were dark-hued muds and light silts in the outcrop, settled from Silurian floods. There were balls and pillows, climbing ripples, flow rolls, and mini-dunes—multihued structures in the river sands. Maroon. Damask. Carmine. Rouge.
Artists were the Delaware Water Gap’s most effective discoverers. Inadvertently, they publicized it. They almost literally put it on the map. Arrested by the symmetries of this geomorphological phenomenon, they sketched, painted, and engraved it. The earliest dated work is the Strickland Aquatint, 1830, with a long and narrow flat-bottomed Durham boat in the foreground on the river, four crewmen standing at their oars, a steersman (also standing) in the stern, and in the background the wildwoods rising up the mountain with its deep, improbable incision.
Cutting and filling, a stream would cross its own valley, gradationally leaving gravels under sands under silts under muds under fine grains that settled in overbank floods. With nothing missing, the sequence was before us now, and was many times reiterated in the rock—a history of the migrations of the stream as it spread layer upon layer through its subsiding valley, 412, 411, 410 million years ago.
In 1832, Asher B. Durand came upon the scene. Durand was one of the founders of what in time wou
ld be labelled the Hudson River School. The term was a pejorative laid by a critic on painters who went outdoors to vent their romantic spirits. They went up the Hudson, they went up the Rockies, and they went into the Water Gap unafraid. Durand painted another Durham boat. His trees looked Japanese. The picture was published after Durand himself made a copper engraving. It contributed to the axiom that where an easel had stood a hotel would follow. Kittatinny House was established in 1833, sleeping twenty-five.
Anita chipped out a piece of Bloomsburg conglomerate—evidence in itself that the stream which had made it was by no means spent. The rolling Silurian countryside must have been lovely—its river valleys velvet green. There were highland jaspers among the pebbles in the sand.
The early geologists began arriving in 1836, led by Henry Darwin Rogers. They were conducting Pennsylvania’s first geological survey. In the deep marine Martinsburg slate and in the mountain strata that stood above it—in the “plication” and the “corrugation” of the sediments—Rogers saw “stupendous crust-movement and revolution,” the “most momentous” of ancient times, and reported to Harrisburg what would eventually become known as the Taconic and Alleghenian orogenies. He decided that something had wrenched the mountain in New Jersey several hundred feet out of line with its counterpart in Pennsylvania. “I conceive these transverse dislocations to pervade all the great ridges and valleys of our Appalachian region,” he wrote, “and to be a primary cause of most, if not all, of those deep notches which are known by the name of Water Gaps, and which cleave so many of our high mountain ridges to their very bases.”
