Annals of the Former World

by John McPhee

  If you had turned around and gone back to Nevada a million years later, still in Meramecian time, there would have been few variations to note along the way. The west coast would have moved east, but only a bit, and would still be approximately at the western end of Wyoming. There would have been a significant alteration, however, in the demeanor of the island over the strait. At a little over two inches a year, it would have moved forty miles or so eastward, compressing the floor of the strait and pushing up high mountains, like the present mountains of Timor, which have come up in much the same way to stand ten thousand feet above the Banda Sea. Up from the sea and within those Meramecian Nevada mountains came the wine-red pebbly sandstone of the Tonka formation.

  Forty million years after that, when the Tonka mountains had been worn flat and the Strathearn limestones were forming over their roots, the American scene was very different. It was now the Missourian age of late Pennsylvanian time (about three hundred million years ago), and the Appalachians were still high but they were no longer alpine. Travelling west, and coming down from the mountains around Du Bois, Pennsylvania, you would have descended into a densely vegetal swamp. This was Pennsylvania in the Pennsylvanian, when vegetation rioted on the earth and the big trees were kings. They were not huge by our standards but they were big trees, some with diamond patterns precisioned in their bark. They had thick boles and were about a hundred feet high. Other trees had bark like the bark of hemlocks and leaves like flat straps. Others had the fluted, swollen bases of cypress. In and out among the trunks flew dragonflies with the wingspans of great horned owls. Amphibians not only were walking around easily but some of them had become reptiles. Through the high meshing crowns of the trees not a whole lot of light filtered down. The understory was all but woven—of rushlike woody plants and seed ferns. There were luxuriant tree ferns as much as fifty feet high. The scene suggests a tropical rain forest but was more akin to the Everglades, the Dismal Swamp, the Atchafalaya basin—a hummocky spongy landscape ending in a ragged coast. All through Pennsylvanian time, ice sheets had been advancing over the southern continents, advancing and retreating, forming and melting, lowering and raising the level of the sea, and as the sea came up and over the land in places like the swamps of Du Bois it buried them, first under beach sand and later—as the seawater deepened—under lime muds. With enough burial, the muds became limestone, the sands became sandstone, the vegetation coal. When the sea fell, erosion wore away some of that, but then the sea would rise again to bury new generations of ferns and trees under successive layers of rock. These cyclothems, as they are called, contain the coals of Pennsylvania, and similar ones the coals of Iowa and Illinois. The shallow sea that reached into western Pennsylvania and eastern Ohio was a hundred miles wide in the Missourian age of Pennsylvanian time, and after crossing the water you would have reached a beach and another coal swamp and then, in light-gray soil, a low lush tropical forest that went on through Indiana to eastern Illinois, where it ended with more coal swamps, another sea. The far shore was where the Mississippi River is now, and beyond that was an equatorial rain forest, which ended in central Iowa with another swamp, another sea. The water here was clear and sparkling, with almost no land-derived sediments settling into it, just accumulating skeletons—clean deep beds of lime. Five hundred miles over the water, you would have raised the rose-colored beaches of eastern Wyoming. Mountains stood out to the south. They were the Ancestral Rockies, and time would bevel them to stumps. Skirting them, in Pennsylvanian Wyoming, you would have traversed what seem to have been Saharan sands, wave after wave of dunal sands, five hundred miles of rose and amber pastel sands, ending at the west coast of North America, in Salt Lake City. As the Pennsylvanian sea level moved up and down here, it left alternating beds of lime and sand, which, two eras later, the nascent Oquirrh Mountains would lift to view. Two hundred miles out to sea was the site of Carlin Canyon, where muds of clean lime were settling. The Strathearn, the younger formation of the two in the Carlin unconformity, is an almost pure limestone.

  The two formations, conjoined, were driven upward, according to present theory, in a collision of crustal plates that occurred in the early Triassic. The result was yet another set of new mountains—alpine mountains which erosion brought down before the end of the Jurassic, but not enough to obliterate the story that is told in Carlin Canyon. Still gazing at the Carlin unconformity, Ken Deffeyes said, “Profound as all the time is to build and destroy those mountain ranges, it is just a one-acter in the history of the Basin and Range —small potatoes, weak beer, just a little piece of time, a little piece of the action, lost in all the welter of all the other history.” There had been two complete cycles of erosion and deposition and mountain building in this one place in one-fortieth of the time scale. That is what made John Playfair’s mind grow giddy when James Hutton took him in 1788 to see the angular unconformity at Siccar Point. It was especially fortunate that Playfair was there, and that Playfair knew Hutton and Hutton’s geology equally well, for when Hutton finally wrote his book most readers were trampled by the prose. Hutton was at best a difficult writer. Insights came to him but phrases did not. James Hall, who was twenty-seven when he went with Hutton and Playfair to Siccar Point, would say of Hutton years later, “I must own that on reading Dr. Hutton’s first geological publication I was induced to reject his system entirely, and should probably have continued still to do so, with the great majority of the world, but for my habits of intimacy with the author, the vivacity and perspicuity of whose conversation formed a striking contrast to the obscurity of his writings.” Hall, incidentally, melted rock in crucibles and saw how crystals formed as it cooled. He is regarded as the founder of experimental geology. John Playfair likewise assessed Hutton’s literary style as containing “a degree of obscurity astonishing to those who knew him, and who heard him every day converse with no less clearness and precision than animation and force.” One can imagine what Playfair thought when he read something like this in Hutton’s two-volume Theory of the Earth:

  If, in examining our land, we shall find a mass of matter which had been evidently formed originally in the ordinary manner of stratification, but which is now extremely distorted in its structure and displaced in its position,—which is also extremely consolidated in its mass and variously changed in its composition,—which therefore has the marks of its original or marine composition extremely obliterated, and many subsequent veins of melted mineral matter interjected; we should then have reason to suppose that here were masses of matter which, though not different in their origin from those that are gradually deposited at the bottom of the ocean, have been more acted upon by subterranean heat and the expanding power, that is to say, have been changed in a greater degree by the operations of the mineral region.

  In that long sentence lies the discovery of metamorphic rock. But just as metamorphism will turn shale into slate, sandstone into quartzite, and granite into gneiss, Hutton had turned words into pumice. Unsurprisingly, his insights did not at once spread far and wide. They received a scattered following and much abuse. The attacks were theological, in the main, but, needless to say, geological as well—particularly with regard to his elastic sense of time. Even when people began to agree that the earth must be a great deal older than six thousand years, calculations were conservative and failed to yield the reach of time that Hutton’s theory required. Lord Kelvin, as late as 1899, figured that twenty-five million years was the approximate age of the earth. Kelvin was the most august figure in contemporary science, and no one stepped up to argue. Hutton published his Theory of the Earth in 1795, when almost no one doubted the historical authenticity of Noah’s Flood, and all species on earth were thought to have been created individually, each looking at the moment of its creation almost exactly as it did in modern times. Hutton disagreed with that, too. Writing a treatise on agriculture, he brought up the matter of variety in animals and noted, “In the infinite variation of the breed, that form best adapted to the exercise of the instin
ctive arts, by which the species is to live, will most certainly be continued in the propagation of this animal, and will be always tending more and more to perfect itself by the natural variation which is continually taking place. Thus, for example, where dogs are to live by the swiftness of their feet and the sharpness of their sight, the form best adapted to that end will be the most certain of remaining, while those forms that are less adapted to this manner of chase will be the first to perish; and, the same will hold with regard to all the other forms and faculties of the species, by which the instinctive arts of procuring its means of substance may be pursued.” When he died, in 1797, Hutton was working on that manuscript, no part of which was published for a hundred and fifty years.

  People who admired Hutton’s theory of the earth became known—because of the theory’s igneous aspects, its molten basalts and intruding granites—as vulcanists or plutonists, and they quickly grew to be the intellectual enemies of the Wernerian neptunists, and others who believed that God had made the world through a series of catastrophes, notably the Noachian flood. The schism between these two groups would carry well into the nineteenth and even into the twentieth century, the ratio gradually reversing. In 1800, the Huttonians were outnumbered at least ten to one. In fact, a Wernertrained neptunist took over the chair of natural history at the University of Edinburgh and for many years neptunism was official in Hutton’s own city.

  All this can be presumed to have bestirred John Playfair, a handsome, life-loving, and generous man of “mild majesty and considerate enthusiasm,” as a contemporary described him. Never mind that the contemporary was his nephew. With all those neptunists and men of the cloth on the one side and his friend’s prose on the other, the battle to Playfair must have seemed unjust, and he betook himself to alter the situation. The least of his many verbal gifts was a slow-cooled lucidity, a sense of the revealing phrase, and his Illustrations of the Huttonian Theory of the Earth, published in 1802, was the first fully clear and persuasive statement of what the theory was about. It is testimony to Playfair’s efficacity that the opposition stiffened. “According to the conclusions of Dr. Hutton, and of many other geologists, our continents are of indefinite antiquity, they have been peopled we know not how, and mankind are wholly unacquainted with their origin,” wrote the Calvinist geologist Jean Andre Deluc in 1809. “According to my conclusions, drawn from the same source, that of facts, our continents are of such small antiquity, that the memory of the revolution which gave them birth must still be preserved among men; and thus we are led to seek in the book of Genesis the record of the history of the human race from its origin. Can any object of importance superior to this be found throughout the circle of natural science?”

  As geologists built the time scale, their research and accumulating data imparted to Hutton’s theory an obviously increasing glow. And in the early eighteen-thirties Charles Lyell, who said in so many words that his mission in geology was “freeing the science from Moses,” gave Hutton’s theory and his sense of deep time their largest advance toward universality. In three volumes, he published a work whose full title was Principles of Geology, Being an Attempt to Explain the Former Changes of the Earth’s Surface, by Reference to Causes Now in Operation. Lyell was so anti-neptunist, so anti-catastrophist that he out-Huttoned Hutton both in manner and in form. He not only subscribed to the uniformitarian process—the topographical earth building and destroying and rebuilding itself through time—but was finicky in insisting that all processes had been going on at exactly the same rate through all ages. Principles of Geology was to be the most enduring and effective geological text ever published. The first volume was eighteen months off the press when H.M.S. Beagle set sail from Devonport with Charles Darwin aboard. “I had brought with me the first volume of Lyell’s Principles of Geology, which I studied attentively; and the book was of the highest service to me in many ways. The very first place which I examined, namely St. Jago in the Cape de Verde islands, showed me clearly the wonderful superiority of Lyell’s manner of treating geology, compared with that of any other author whose works I had with me or ever afterwards read.” When Darwin had first studied geology, he had heard lectures in Wernerian neptunism at Edinburgh, and they had very nearly put him to sleep. Nevertheless, the degree he later took at Cambridge University was in geology. He referred to himself as a geologist. His field identifications of the rocks he collected on his travels, and of the minerals within the rocks, were essentially without error. The rocks are in Cambridge, where contemporary geologists have thin-sectioned them, confirming Darwin’s petrology. Voyaging on the Beagle, he was enhancing his sense of the slow and repetitive cycles of the earth and the giddying depths of time, with Lyell’s book in his hand and Hutton’s theory in his head. In six thousand years, you could never grow wings on a reptile. With sixty million, however, you could have feathers, too.

  According to present theory, many exotic terranes moved in from the western ocean and collected against North America during a span of about three hundred million years which ended roughly forty million years ago, increasing the continent to something like its present size. Three of these assembled at the latitude of Interstate 80. It was the first of these collisions that crunched and folded the wine-red sandstone near Carlin. The second, in the early Triassic, is what apparently caused the whole Carlin unconformity to revolve quite close to its present position. Sonomia, as the second terrane has been named, included much of what is now western Nevada and eastern California, and is said to have come into the continent with such force—notwithstanding that it was moving an inch or so a year—that it overlapped its predecessor by as much as eighty kilometres before it finally stopped. The evidence of this event is known locally as the Golconda Thrust, and both its upper and lower components are exposed in a big roadcut on the western flank of Golconda Summit, where the interstate, coming up out of Pumpernickel Valley, crosses a spur of the Sonoma Range. Small wonder that Deffeyes pulled over when we came to it and said, “Let’s stick our eyeballs on this one.”

  It was dawn at the summit. We had been awake for hours and had eaten a roadhouse breakfast sitting by a window in which the interior of the room was reflected against the black of the morning outside while a television mounted on a wall behind us resounded with the hoofbeats of the great horse Silver. The Lone Ranger. Five A.M. CBS’s good morning to Nevada. Waiting for bacon and eggs, I put two nickels in a slot machine and got two nickels back. The result was a certain radiance of mood. Deffeyes, for his part, was thinking today in troy ounces. It would take a whole lot more than two nickels to produce a similar effect on him. Out for silver, he was heading into the hills, but first, in his curiosity, he walked the interstate roadcut, now and again kicking a can. The November air was in frost. He seemed to be smoking his breath. He remarked that the mean distance between beer cans across the United States along I-80 seemed to be about one metre. Westward, tens of hundreds of square miles were etched out by the early light: basins, ranges, and—below us in the deep foreground—Paradise Valley, the village Golconda, sinuous stands of cottonwood at once marking and concealing the Humboldt. The whole country seemed to be steaming, vapors rising from warm ponds and hot springs. The roadcut was long, high, and benched. It was sandstone, for the most part, but at its lower, westernmost end the blasting had exposed a dark shale that had been much deformed and somewhat metamorphosed, the once even bedding now wrinkled and mashed—rock folded up like wet laundry. “You can spend hours doping out one of these shattered places, just milling around trying to find out what’s going on,” Deffeyes said cautiously, but he was fairly sure he knew what had happened, for the sandstone that lay above contained many volcanic fragments and was full of sharp-edged grains of chert and quartz, highly varied in texture, implying to him a volcanic source and swift deposition into the sea (almost no opportunity for streams to have rounded off the grains), implying, therefore, an island arc standing in deep water on a continental margin—an Aleutian chain, a Bismarck Archipelago, a
Lesser Antilles, a New Zealand, a Japan, thrust upon and overlapping the established continent, a piece of which was that mashed-up shale. Deffeyes mused his way along the cut. “There is complexity here because you have not only the upper and lower plates of the Golconda Thrust, which happened in the early Triassic; you also have basin-range faulting scarcely a hundred yards away—enormously complicating the regional picture. If you look at a geologic map of western Canada and Alaska, you can see the distinct bands of terrane that successively attached themselves to the continent. Here the pattern has been all broken up and obscured by the block faulting of the Basin and Range, not to mention the great outpouring of Oligocene welded tuff. So this place is a handsome mess. If you ever want to study this sort of collision more straightforwardly, go to the Alps, where you had a continent-to-continent collision and that was it.”