Annals of the Former World

by John McPhee

  Of course, plenty of heat is produced by deep burial during major tectonic events. Her conodonts from New Jersey were black and from Kentucky pale essentially because huge disintegrating eastern mountain ranges had buried the near ones very deep and the far ones scarcely at all. The East is for the most part the wreckage of the Ancestral Appalachians, and—as is exemplified in the Devonian rock of New York—the formations are thickest close to where the mountains stood. A continuous sedimentary deposit that is thousands of feet thick in eastern Pennsylvania may be ten feet thick in Ohio. Where oil was first discovered in western Pennsylvania, it was seeping out of rocks and running in the streams. It is of a character and purity so remarkable that people used to buy it and drink it for their health. Anita looked at conodont samples from rock that surrounded this truly exceptional oil. In the temperature range of eighty to a hundred and twenty degrees, they were in the center of the petroleum window. They were golden brown.

  With a year of tests run, with Kodachrome pictures, with graphs and charts of what she called her “wind-tunnel models,” she was prepared to tell her story. The Geological Society of America was to meet in Florida in November, 1974, and she arranged to deliver a paper there. “I prepared carefully—I always do—so I wouldn’t phumpfer. But the G.S.A. meeting was not momentous. They were academics, and not particularly knowledgeable about exploration techniques.” Five months later, scarcely knowing what to anticipate, she went to Dallas and spoke before the American Association of Petroleum Geologists. It was the same show, but this time it was playing in the right house. Requests and invitations poured upon her from oil companies wherever they might be, and from geological societies situated in oil centers like Calgary and Tulsa. “It filled a big hole in their technology,” Anita has said, recalling those days. “They have to be able to assess the thermal level of deposits, and this was a simple way to do it.”

  Anita became a conodont specialist for the United States Geological Survey, full time. She lives in Maryland. Her home is an island in flower beds and lawn. She gets up at four-thirty and drives to work at the Survey’s headquarters in Reston, Virginia. Oil companies have continued to beat the path to her door, as have oil geologists from every continent but Antarctica, including large delegations from the Chinese Geological Survey. While oil prospectors are using brown and yellow conodonts to guide them to the thermal window, mineral prospectors are using white ones in the search for copper, iron, silver, and gold. White conodonts and clear conodonts, products of the highest temperatures, suggest the remains of thermal hot spots, thermal aureoles, ancient hydrothermal springs—places where metallic minerals would have come up in solution to be precipitated out into veins.

  Soon after her discovery, universities began calling her. She was pleased to appear at places like Princeton, pleased to be given an opportunity to demonstrate what could be learned elsewhere. Women students were in her audience now. In the late nineteen-seventies, she and her colleagues published a succession of scientific papers whose title pages perforce encapsulated not only their professional endeavors but something of their private lives. The “senior author” of a scientific publication is the person whose name is listed first and whose work has been of primary importance to the project, while other authors are listed more or less in diminishing order, like the ingredients on a can of stew. The benchmark paper came in 1977. Entitled “Conodont Color Alteration—an Index to Organic Metamorphism,” it was “by Anita G. Epstein, Jack B. Epstein, and Leonard D. Harris.” Then, in 1978, came “Oil and Gas Data from Paleozoic Rocks in the Appalachian Basin: Maps for Assessing Hydrocarbon Potential and Thermal Maturity (Conodont Color Alteration Isograds and Overburden Isopachs)”—virtually an oil-prospecting kit, a highly specialized atlas—“by Anita G. Harris, Leonard D. Harris, and Jack B. Epstein.” And scarcely a year after that appeared a summary document called “Conodont Color Alteration, an Organo-Mineral Metamorphic Index, and Its Application to Appalachian Basin Geology”—“by Anita G. Harris.”

  Anita Harris—beginning her trip west on Interstate 80 with her rock hammer, her sledgehammer, her hydrochloric acid, and me—stopped at a lookoff near Allamuchy, New Jersey, about five miles west of Netcong. It was a cool April morning, the tint of the valley pastel green, and from our relatively high perspective, at an altitude of a thousand feet, the eye was drawn eighteen miles west across a gulf of air to the forested wall of Kittatinny Mountain, filling the skyline of two states, its apparently endless flat ridgeline broken only by one deep notch, which centered and arrested the view and was as sharply defined as a notch in a gunsight: the Delaware Water Gap, where the big river comes obliquely through the mountain, like a thief through a gap in a fence. There was a ridge or two near and below us, but the distance to the Water Gap was occupied largely by the woodlots, hedgerows, and striped fields of a broad terrain as much as seven hundred feet lower than the spot on which we stood and of such breathtaking proportions and fetching appearance that it could be mentioned in a sentence with the Shenandoah Valley. The picture of New Jersey that most people hold in their minds does not include a Shenandoah Valley. Nevertheless, this New Jersey Appalachian landscape not only looked like the Shenandoah, it actually was the Shenandoah, in the sense that it was a fragment of a valley that runs south from New Jersey to Alabama and north from New Jersey into Canada—a single valley, one continuous geology, known to science as the Great Valley of the Appalachians and to local peoples here and there as Champlain, Shenandoah, Tennessee Valley, but in New Jersey by no special name. This integral, elongate, predominantly carbonate valley disappears and reappears through the far Northeast, until in pieces it presents itself in Newfoundland and then dives under the sea. Its marbles are minable in Vermont, in Tennessee. It was the route of armies—the avenue to Antietam, the site of Chickamauga, Saratoga, Ticonderoga. It stands in the morning shadow of the Annieopsquotch Mountains, of the Green Mountains, of the New Jersey Highlands, of the Berkshire, Catoctin, and Great Smoky Mountains, which are fraternal in structure and composition and are all of Precambrian age. The lookoff where we stood was a part of that Appalachian complex. It was crystalline rock above a thousand million years old—and the rock in the valley was younger, and in the Kittatinny younger still. (Geologists avoid the word “billion” because in one part and another of the English-speaking world the quantity it refers to differs by three orders of magnitude. A billion in Great Britain is a million million.) We were looking from the New Jersey Highlands into another segment of the cordillera—the beginnings of the physiographic Ridge and Valley Province, the folded-and-faulted deformed Appalachians, the long ropy ridges of the eastern sinuous welt, which Edmund Wilson had once written off as “fairly unimportant creases in the earth covered with trees.”

  “Geology repeats itself,” Anita remarked, and she went on to say that anyone who could understand the view before us would have come to understand in a general way the Appalachians as a whole—that what we were looking at was the fragmental evidence and low remains of alpine massifs immeasurably high and wide, massifs which for the most part had stood behind us to the east, and were now largely disintegrated and recycled into younger rock that is tens of thousands of feet deep and wedges out to the west in ever-diminishing quantity until what covers Ohio is a thin veneer.

  The appearance of a country is the effect primarily of water, running off the landscape, cutting out valleys, dozing wantonly as glacier ice. The sculpturing is external. But it is influenced and can even be controlled by the rock within: by the relative strength, not to mention the solubility, of successive strata, and by the folds and faults—the structure—that the rock has been given. Figuring out the Appalachians was Problem 1 in American geology, and a difficult place to begin, for it was scarcely a matter of layer-cake legibility, like the time scale in the walls of the Grand Canyon. It was a compressed, chaotic, ropy enigma four thousand kilometres from end to apparent end, full of overturned strata and recycled rock, of steep faults and horizontal thrust sheets,
of folds so tight that what had once stretched twenty miles might now fit into five. The country seemed to consist of parallel meandering belts—the Piedmont, the Precambrian highlands, the Great Valley, the folded-and-faulted deformed mountains, the Allegheny Plateau. It was high and resistant, low and vulnerable. (I have heard the Shenandoah described, if not dismissed, as “a strip of weak rock.”) The early Appalachian geologists, in their horse-drawn buggies, their suits and ties, developed a sense of physiography that tuned them to the land, and when they saw long sugarloaf hills they had learned to suspect that there was dolomite within, and when they looked up at coxcomb ridges they felt the presence of Cambrian sandstones, and of Cambrian shales in the valleys beyond. The higher, harder ridges would be thick, Silurian quartzites, more often than not, while flourishing green lowlands with protruding ribs of rock would owe their shape and their fertility to limestones assembled in Ordovician seas. There were knolls in the valleys. Inside the knolls were shales. Shale breaks up easily but will not dissolve like limestone, so the shales became blisters in the limestone valleys. Of the two carbonate rocks, limestone is a good deal more soluble than dolomite, and that was why dolomite would retain itself in sugarloaves above the limestone valleys. Once the early geologists had developed this sense of the substrate, they shook the reins and moved with dispatch, filling in the first American geologic maps with a general accuracy that is impressive still.

  Identifying what is there scarcely describes what happened to put it there, however. The history of the earth may be written in rock, but history is not coherent on a geologic map, which shows a region’s uppermost formations in present time, while indicating little of what lies farther down and less of what is gone from above. At a given place—a given latitude and longitude—the appearance of the world will have changed too often to be recorded in a single picture, will have been, say, at one time below fresh water, at another under brine, will have been mountainous country, a quiet plain, equatorial desert, an arctic coast, a coal swamp, and a river delta, all in one Zip Code. These scenes are discernible in, among other things, the sedimentary characteristics of rock, in its chemical composition, magnetic components, interior color, hardness, fossils, and igneous, metamorphic, or depositional age. But as parts of the historical narrative these items of evidence are just phrases and clauses, often wildly disjunct. They are like odd pieces from innumerable jigsaw puzzles. The rock column—a vertical representation of the crust at some point on the earth—holds a great deal of inferable history, too. But rock columns are generalized; they are atremble with hiatuses; and they depend in large part on well borings, which are shallow, and on three-dimensional seismic studies, which are new, and far between. To this day, in other words, there remains in geology plenty of room for the creative imagination. All the more amazing is the extent to which the early geologists, who travelled the Appalachians in the eighteen-twenties and thirties, not only catalogued the evident rock but also worked out stratigraphic relationships among various formations and began to see composite structure. Starting close up, with this rock type, that mountain, this formation, that valley—with what they could see and know—they gradually began to form tentative regional pictures. Piece by piece over the next century and a half, they and their successors would put together logically sequential narratives presenting the comprehensive history of the mountain belt. As new evidence and insight came along, old logic sometimes fell into discard. When plate tectonics arrived, its revelations were embraced or accommodated but by no means universally accepted. The Appalachians, meanwhile, continued slowly to waste away. The debate about their origins did not.

  Observing the valley scene, the gapped and distant ridgeline, Anita said that mountains in this region had come up and been worn down not once but a number of times: the Appalachians were the result of a series of pulses of mountain building, the last three of which had been spaced across two hundred and fifty million years —the Taconic Orogeny, the Acadian Orogeny, and the Alleghenian Orogeny. The first stirrings of the Taconic Orogeny began nearly five hundred million years ago. After the mountains it lifted had been largely eroded away, their stubs and their detritus, much of which had turned into sedimentary rock, became involved in the Acadian Orogeny; and when the Acadian Orogeny was long gone by, its mountain stubs and lithified debris were caught up in the Alleghenian Orogeny, which drove into the sky still another massif, the ruins of which lay all about us now. In such manner had each of the orogenies of the Appalachians cannibalized the products of previous pulses, and now we were left with this old mountain range, by weather almost wholly destroyed, but nonetheless containing in a traceable and unarguable way the rock of its ancestral mountains. She said the Delaware Water Gap, with its hard quartzites, represented action from the heart of the story, debris from the Taconic Orogeny: boulders, pebbles, sands, and silts carried down from bald mountains by the rapids of big braided rivers—a runoff unimpeded by vegetation, when not so much as one green leaf existed in the terrestrial world.

  Long before the Taconic mountain-building pulse was felt, the scene was very different. A subdued continent, consisting of what is now the basement rock of North America, stood low with quiet streams, collecting on its margins clean accumulations of sand. One can infer the flat landscape, the slow rivers, the white beaches, in the rock that remains from those Cambrian sands. Sea level, never constant, moved generally upward all through Cambrian time. The water advanced upon the continent at an average rate of ten miles every million years, spreading across the craton successive coastal sands. Potsdam sandstone. Antietam sandstone. Waynesboro sandstone. Eau Claire sandstone. There were fifty-four million years in the long tectonic quiet of Cambrian time, 544 to 490 million years before the present. By the end of the Cambrian and the beginning of the Ordovician, the ocean had spread its great bays upon the continents to an extent that has not been equalled in five hundred million years, with the possible exception of the highest Cretaceous seas. No one knows why. There is a fixed amount of water in the world. It can rain and run, evaporate, freeze, sit in deep cold pools on abyssal plains, but it cannot leave the earth. When large amounts of it collect as ice upon the continents, the level of the sea drastically goes down. In much of Cambro-Ordovician time, glaciation was absent from the world, and almost all water was in a fluid state. But that alone will not explain the signal height of the sea. In most of the known history of the earth, glacial ice has actually been insignificant. Ice ages, such as the present one, are extremely rare. What seems likely is that ocean floors were higher in Cambro-Ordovician time, fluffed up by more than the usual amount of heat from the restless mantle—heat of the sort that has created the Hawaiian Islands in the middle of a lithospheric plate, and heat of the sort that lifts mid-ocean ridges, where plates diverge. Whatever the reason, the sea came up so far that it covered more than half of what is now the North American craton. And after the white clean beaches and shelf sands had spread their broad veneer, lime muds began to accumulate in the epicratonic seas. The lime muds were the skeletons, the macerated shells, the calcareous hard parts of marine creatures. The material turned into limestone, and where conditions were appropriate the limestone, infiltrated by magnesium, became dolomite. As the deposit grew to a general thickness of two thousand feet, these Cambro-Ordovician carbonates buried ever deeper the sandstone below them and the Precambrian rock below that, pressing it all downward like the hull of a loading ship, into the viscous mantle—but sedately, calmly, a few inches every thousand years.

  Absorbing the valley scene, the gapped and distant ridgeline, the newly plowed fields where arrowheads appear in the spring, I remarked that we had entered the dominion of the Minsi, the northernmost band of the Lenape. They came into the region toward the dawn of Holocene time and lost claim to it in the beginnings of the Age of Washington. Like index fossils, they now represent this distinct historical stratum. Their home and prime hunting ground was the Minisink—over the mountain, beside the river, the country upstream from the gap.
The name Delaware meant nothing to them. It belonged to a family of English peers. The Lenape named the river for themselves. I knew some of this from my grade-school days, not many miles away. The Minisink is a world of corn shocks and islands and valley mists, of trout streams and bears, today. Especially in New Jersey, it has not been mistreated, and, with respect to the epoch of the Minsi, geologically it is the same. The Indians of the Minisink were good geologists. Their trails ran great distances, not only to other hunting parks and shell-mounded beach camps but also to their quarries. They set up camps at the quarries. They cooked in vessels made of soapstone, which they cut from the ground in what is now London Britain Township, Chester County, Pennsylvania. They made adzes of granite, basalt, argillite, even siltstone, from sources closer to home. They went to Berks County, in Pennsylvania, for gray chalcedony and brown jasper. They used glacial-erratic hornfels. They made arrowheads and spear points of Deepkill flint. They made drills and scrapers of Onondaga chert. Flint, chert, and jasper are daughters of chalcedony, which in turn is a variety of quartz. The Eastern flint belt runs from Ontario across New York State and then south to the Minisink. The Indians did not have to attend the Freiberg Mining Academy to be able to tell you that. They understood empirically the uniform bonding of cryptocrystalline quartz, which cannot be separated along flat planes but fractures conchoidally, by percussion, and makes a razor’s edge. The forests were alive with game on the sides of what the Lenape called the Endless Mountain. There were eels, shad, sturgeon in the river. The people lived among maize fields in osier cabins. They worshipped light and the four winds—all the elements of nature, orchestrated by the Great Manito. The burial grounds of the Minsi display the finest vistas in the Minisink. As the dead were placed in the earth, they began their final journey, through the Milky Way.