by John McPhee
The group was known as Agassiz’s Club, more officially as the Saturday Club. One summer, when the club went off to the Adirondacks on a camping trip, Longfellow refused to go, because Emerson was taking a gun. “Somebody will be shot,” said Longfellow, explaining that Emerson was too vague to be trusted with a gun. Longfellow’s works of poetry include a birthday ballad in praise of Agassiz, which Longfellow read aloud at the Saturday Club, and in which Nature addressed the Professor:
“Come wander with me,” she said,
“Into regions yet untrod;
And read what is still unread
In the manuscripts of God.”
John Greenleaf Whittier also wrote a poem about Agassiz, more than a hundred lines in length, ten of which are these:
Said the Master to the youth:
“We have come in search of truth,
Trying with uncertain key
Door by door of mystery;
We are reaching, through His laws,
To the garment-hem of Cause,
Him, the endless, unbegun,
The unnanwable, the One
Light of all our light the Source,
Life of life, and Force of force.”
Longfellow, travelling in Europe in 1868, called on Charles Darwin. “What a set of men you have in Cambridge,” Darwin said to him. “Both our universities put together cannot furnish the like. Why, there is Agassiz—he counts for three.”
Darwin’s generosity was remarkable in the light of Agassiz’s reaction to The Origin of Species. As Agassiz summarized it: “The world has arisen in some way or other. How it originated is the great question, and Darwin’s theory, like all other attempts to explain the origin of life, is thus far merely conjectural. I believe he has not even made the best conjecture possible in the present state of our knowledge.” Agassiz never accepted Darwinian evolution. Many years earlier, as a young man, and as a result of his paleontological researches, he wrote the following:
More than fifteen hundred species of fossil fishes with which I have become acquainted say to me that the species do not pass gradually from one to the other, but appear and disappear suddenly without direct relations with their predecessors; for I do not think that it can be seriously maintained that the numerous types of Cycloids and Ctenoids, which are nearly all contemporaneous with each other, descend from the Placoids and Ganoids. It would be as well to affirm that the mammals, and man with them, descend directly from fishes. All these species have a fixed time for coming and going; their existence is even limited to a determined period. And still they present, as a whole, numerous, and more or less close affinities, a determined coördination in a system of organization which has an intimate relation with the mode of existence of each type, and even of each species. More still: there is an invisible thread which is unwinding itself, through all the ages, in this immense diversity, and offers as a final result a continuous progress in this development of which man is the termination, of which the four classes of vertebrates are the intermediate steps, and the invertebrates the constant accessory. Are not these facts manifestations of a thought as rich as it is powerful, acts of an intelligence as sublime as provident? … This is, at least, what my feeble intellect reads in the works of creation … . Such facts loudly proclaim principles which science has not yet discussed, but which paleontological researches place before the eyes of the observer with increasing persistency; I mean the relation of the Creation to the Creator.
Nothing that occurred during the rest of Agassiz’s life caused him to revise what he had said. He died in 1873. Harvard appointed three professors to replace him. Nine years later, in a scientific journal Agassiz had founded, his successor in the chair of geology published a paper describing the Ice Age as a myth. “The so-called glacial epoch … so popular a few years ago among glacial geologists may now be rejected without hesitation,” the article concluded. “The glacial epoch was a local phenomenon.”
West of Cleveland, the terrain became increasingly flat. High outcrops disappeared, but now and again a blocky strip of rock would run along the road like a retaining wall—a glimpse of what underlay the surrounding fields. Berea sandstone. Bedford shale. Columbus limestone. “You could map this state at sixty miles an hour,” Anita said. For some distance, the soil over the rock was fine glacial till—ground rock flour and sand—and then among white farms we moved out upon a black-earth plain where drainage ditches did the work of streams: a world of absolute level, until recently the bottom of a great lake. The limestone had formed in the clear salt sea of middle Devonian tropical Ohio. Eventually, the sea disappeared. Two eons later, ice slid over the limestone and, retreating, left a body of fresh water that included all of what is now Lake Erie and was twice as large.
“We wouldn’t be able to feed this country the way we do if much of it had not been glaciated,” Anita said. “South of the glaciers, ancient weathering removed soluble minerals and left a rather inert soil behind. After a couple of decades of planting, you need tremendous fertilizer additions there. This glacial stuff is full of unweathered mineral material—fresh—ground rock. And under it is limestone, which is what they put on fields. When early settlers came through here and saw no trees, they moved on to places like Missouri, beyond the glacial limit, and they missed some great farmland. In Egypt, they used to get fresh minerals with every flood, but those morons built the Aswan High Dam and stopped the floods. They’re starving themselves out and making a salt pan of the delta.”
We were crossing the Findlay Arch and had reached the edge of the Michigan Basin, features of the subsurface structure, invisible and unexpressed in the black level surface of silts and clays. In tropical Ohio, the arch had at one time held back a large piece of the retreating sea. As the isolated water slowly concentrated and eventually disappeared, it left Morton’s salt and U.S. gypsum. It left even more limestone. It left dolomite, anhydrite—components of what is known as the evaporite sequence. North off the interstate, we went through Gypsum, Ohio, on Sandusky Bay, and on to the lake port Marblehead, where we boarded the Kelleys Island ferry. “VISIT HISTORIC GLACIAL GROOVES,” said a sign beside the ticket booth, and soon, for a stiff toll, we were beating into an even stiffer wind, which was tearing the caps off the waves of Lake Erie. Kelleys Island is about four miles offshore, and other cars on the ferry were stuffed with a month’s worth of groceries. A hundred and twenty people live there, year around, on four and a half square miles, and as we drove across the island we passed stone houses with red and black boulder walls—jaspers and amphibolites plucked up by the ice and brought south from the Canadian Shield.
Kelleys Island stands high because it is a piece of the structural arch. While the Wisconsinan ice sheet was excavating the Great Lakes, reaming out whole networks of streams and carrying away the prominent features of their valleys, it bevelled but could not destroy the resistant structural arch. An engulfed ridge stood up from the bottom of the primal lake. With the weight of the ice gone, all of northern America slowly rebounded. A large part of the water gradually drained away, leaving Kelleys Island dry in the air, sixty feet above the level of Lake Erie.
We passed the island cemetery, its names recorded in limestone. We came to the north shore, where the beginnings of a quarrying operation had revealed how the ice had cut its tracks into the rock. “GLACIAL GROOVES STATE MEMORIAL.” It was as if a giant had drawn his fingers through an acre of soft butter. The grooves were parallel. They were larger than the gutters of bowling lanes. Aggregately, they suggested the fluted shafts of Greek columns. Their compass orientation was northeast-southwest —the established glide path of the moving ice. Nowhere had we seen or would we see more emphatic evidence of continental glaciation, with the obvious exception of the Great Lakes themselves. “If you were to hydraulically flush northern Ohio—wash off the soil from the bedrock—you’d see a hell of a lot of these grooves,” Anita said. “In several hundred years, these won’t be here. Limestone is soft enough to be grooved and hard enough t
o resist weather for a few hundred years. In shale, grooves like these would go quickly. The ice, carrying boulders in its underside—carrying those amphibolites and red jaspers in the people’s houses—tore the hell out of this island. When Agassiz saw things like this, he went bananas.”
There have been glacial geologists, even in the late twentieth century, who have believed that such impressive grooves were gouged by boulders rolling in the Flood. Exceptions notwithstanding, Louis Agassiz’s theory of continental glaciation, like the theory of plate tectonics, achieved with extraordinary swiftness its general acceptance in the world. As Thomas Kuhn has demonstrated in The Structure of Scientific Revolutions, when a novel theory becomes relatively established it defines the patterns of amplifying research for many years and even centuries—until a new theory comes along to overturn the old, until an Einstein appears, outreaching the principles of Newton. Conceivably, the theory of plate tectonics will one day experience a general reformation. The theory of continental glaciation seems less prone to grand revision. The sun itself seems as likely to be banished from the center of the solar system as the ice from the Pleistocene continents. The ice made Lake Seneca, Lake Cayuga—all the so-called Finger Lakes, of western New York—cutting them into stream valleys in exactly the manner in which it cut the fjords of Patagonia, the fjords of Norway, Alaska, and Maine. After the ice quarried the huge quantities of Canadian rock that it dumped in the United States, it melted back and filled the quarries with new Canadian lakes—hundreds of thousands of Canadian lakes. A sixth of all the fresh water on earth is in Canadian ponds, Canadian streams, Canadian rivers, Canadian lakes. In Greenland, Antarctica, and elsewhere, a much greater quantity of fresh water—four times as much—is still imprisoned as ice, leaving precious little fresh water for the rest of the world.
Our Epoque Glaciaire has by now been illuminated by a century and a half of expanded research. Glacial outwash has been identified at the mouth of the Mississippi, six hundred miles from the terminal moraine—a suggestion of the power and the volume of the rivers that melted from the ice. Where the land tilted north and the meltwaters pooled against the glacial front—and where waters were trapped between moraines and retreating ice—gargantuan lakes formed, such as Glacial Lake Maumee, the one of which Lake Erie is all that remains. Lake Michigan is all that remains of Glacial Lake Chicago. Lake Ontario is all that remains of Glacial Lake Iroquois. Lake Winnipeg, Lake Manitoba, the Lake of the Woods are among the remains of a glacial lake whose bed and terraces, stream deltas and wave-cut shores reach seven hundred miles across Saskatchewan, Manitoba, and Ontario, and down into the United States as far as Milbank, South Dakota. With the exception of the Caspian Sea, this one was larger than any lake of the modern world. It was the supreme lake of the American Pleistocene—Glacial Lake Agassiz.
Cold air flowing off the ice sheets caused such heavy precipitation when it encountered warm and humid air to the south that whole regions there filled with water, too. The basins of Nevada became lakes and the ranges among them were islands. Lake Bonneville filled a third of Utah. Huge lakes grew in the Gobi Desert, in Australia’s Great Artesian Basin, in various lowlands across North Africa. There were forests in the Sahara, as fossil pollen shows, and networks of flowing streams. Their dry channels remain.
In North America, where the ice started to go back about twenty thousand years ago, the first vegetation to spring up behind it was tundra. Carbon 14 can date the fossil tundra. The dates, particularly in the East, show a slow, and then accelerating, retreat. After five thousand years, the front was still in Connecticut. In another twenty-five hundred years, it crossed the line to Canada. Human beings, living on the tundra near the ice, perforce were inventive and tough. Culture, in part, was a glacial effect. In response to the ice had come controlled fire, weapons, tools, and fur as clothing. Creativity is thought to have flourished in direct proportion to proximity to the glacier—an idea that must infuriate the equatorial mind. The ice drew back from Britain a geologic instant before the birth of Shakespeare. The fossils of Homo sapiens have never been found in sediments older than the Ice Age.
In the way that scenes of vanished mountains can be inferred from their debris, the vision of continents covered with ice came straightforwardly to Agassiz as the product of reasoning carried backward from evidence through time. It is one thing to say that the ice was there, quite another to say how it got there. If the origin of mountains is sublimely moot, so is the origin of the ice. Characteristically, the prime mover is not well understood. The ice did not come over the world like a can of paint poured out on the North Pole. It formed in places well below the Arctic Circle, and moved out in every direction—including north—until cut off by the unsupportive sea. Geologists call these places spreading centers, the same term they use for the rifted boundaries where plates tectonically divide. To the question “Why did the ice form?” they can answer only with speculation. The phenomenon is obviously rare. A pulsating series of ice sheets seems to have been set up in the discernible history of the world roughly once every three hundred million years. It happens so infrequently that it must be the result of coinciding circumstances that could not stand alone as explanations. There are components fast and slow. The atmosphere has been gradually cooling for sixty million years. Possibly this is explained by the great orogenies that have occurred during that time—the creation of the Rockies, the Andes, the Alps, the Himalaya—and the volcanism that is associated with mountain building. Volcanic ash in the stratosphere reflects sunlight back into space. Also, the weathering of mountains, particularly their granites, brings on a chemical reaction that removes carbon dioxide from the atmosphere, diminishing the greenhouse effect and chilling the earth. In any case, the essential requirement is a cool summer. A little snow from one winter must last into the next. Every forty thousand years, the earth’s axis swings back and forth through three degrees. Summers are cooler when the earth is less tilted toward the sun. The sun, for that matter, is not consistent in the energy it produces. Moreover, the relative positions of the sun and the earth, in their lariat voyage through time, vary, too—enough for subtle influence on climate. Carbon dioxide also affects climate, and the amount of carbon dioxide in the atmosphere is not constant. Somewhere in such a list, which runs to many items, lie the simultaneous events that set the ice to growing. The change they bring is not at first dramatic. So critical is the earth’s temperature that a drop of just a few degrees will cause ice to form and spread. A cool summer. Unmelted snow. An early fall in some penarctic valley. An overlap of snow. A long winter. A new cool summer. An enlarged residue of snow. It compacts and recrystallizes into granules, into ice. Because it is white, it repels the sun’s heat and helps cool the air on its own. The process is self-enlarging, unstoppable, and once the ice is really growing it moves. Clear bands form near the base, along which the ice shears and slides upon itself in horizontal layers like the overthrust Appalachians. The thermal output of the earth melts a thin film of water on the glacier bottom, and the ice slides on that, too. Thrust sheets made of rock also slide on water. The lower part of a glacier is plastic, the upper part brittle—like the earth’s moving plates and the plastic mantle beneath them. Where the brittle glacier surface bends, it cracks into crevasses, into fracture zones, as does the brittle ocean crust (the Clarion Fracture Zone, the Mendocino Fracture Zone). Such fractures are everywhere in the rock of continents, too. In fact, the ridged-and-valleyed surface of almost any flowing glacier is remarkably similar to the sinuous topography of the deformed Appalachian mountains. The continental ice sheet moves toward the equator and keeps on going until it cannot stand the heat. At the latitude of New York City, generally speaking, the ice melts as fast as it advances, and thus it goes no farther, and leaves on Staten Island its terminal moraine. Ocean temperatures will have dropped because of the cold, and therefore the oceans are providing less snow to feed the ice. On all fronts, the ice retreats—not necessarily to disappear. The climate warms. The oceans w
arm. The snow pack thickens in the Great North Woods. A glacier spreads again. Once the pattern is set, the rhythm is relatively steady. For us, the ice is due again in ninety thousand years.
We ran on through Ohio on the bed of the great former lake, Kelleys Island far behind us. Where there had been sand spits reaching into the water, with sandy hooks at their tips, there were farm buildings standing on the dry spits—the high prime ground, a few feet higher than the surrounding fields. Now, at spring plowing time, these things were visible as they would not be for a year again.
And then we went off the lakebed and up into roadcuts of vetch-covered till among the kettles, kames, and drumlins, the Wabash Moraine, the New England landscape of glacial Indiana. “This would be a good place for a golf course,” Anita remarked. “If you want a golf course, go to a glacier.” We left the interstate for a time, the better to inspect the rough country. “I grew up in topography like this—in Brooklyn,” Anita said. “I didn’t know what bedrock meant. You could plot the limit of glaciation in New York City by the subway system. Where it’s underground, it’s behind the glaciation. Where it’s in the moraine and the outwash plain, it’s either elevated or in cuts in the ground.”