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There once may have been 250,000 miles of stone walls in America’s Northeast, stretching farther than the distance to the moon. They took three billion man-hours to build. And even though most are crumbling today, they contain a magnificent scientific and cultural story—about the geothermal forces that formed their stones, the tectonic movements that brought them to the surface, the glacial tide that broke them apart, the earth that held them for so long, and about the humans ...
There once may have been 250,000 miles of stone walls in America’s Northeast, stretching farther than the distance to the moon. They took three billion man-hours to build. And even though most are crumbling today, they contain a magnificent scientific and cultural story—about the geothermal forces that formed their stones, the tectonic movements that brought them to the surface, the glacial tide that broke them apart, the earth that held them for so long, and about the humans who built them.
Stone walls tell nothing less than the story of how New England was formed, and in Robert Thorson’s hands they live and breathe. “The stone wall is the key that links the natural history and human history of New England,” Thorson writes. Millions of years ago, New England’s stones belonged to ancient mountains thrust up by prehistoric collisions between continents. During the Ice Age, pieces were cleaved off by glaciers and deposited—often hundreds of miles away—when the glaciers melted. Buried again over centuries by forest and soil buildup, the stones gradually worked their way back to the surface, only to become impediments to the farmers cultivating the land in the eighteenth century, who piled them into “linear landfills,” a place to hold the stones. Usually the biggest investment on a farm, often exceeding that of the land and buildings combined, stone walls became a defining element of the Northeast’s landscape, and a symbol of the shift to an agricultural economy.
Stone walls layer time like Russian dolls, their smallest elements reflecting the longest spans, and Thorson urges us to study them, for each stone has its own story. Linking geological history to the early American experience, Stone by Stone presents a fascinating picture of the land the Pilgrims settled, allowing us to see and understand it with new eyes.
European settlement of New England began not in 1620 when the Pilgrims dropped anchor in Cape Cod Bay, but in 1607, the same year the Jamestown Colony was established in Virginia. The initial attempt at a permanent New England settlement-called the North Virginia Company-took place at Sagadahoc, Maine, on the inner coast north of what is now Portland. There the climate was rigorous; winters were especially difficult. The terrain was rocky, with plentiful bedrock ledges, steep bluffs, stony soils, narrow marshes, and streams. Everyone left within a year. The Sagadahoc settlement had failed, perhaps because its landscape was too cold and hard, too different from that of the mother country, England.
The English returned to the region in 1620, landing much farther to the south, near Plymouth, in what is now southeastern Massachusetts. This group of religious dissidents, later known as the Pilgrims, disembarked the Mayflower to encounter terrain less rocky than that in Maine and a climate less hostile to survival. Times were hard, but the Pilgrims persisted. They proved that life north of the Virginia colonies was possible, if only barely.
A decade later, thethird English migration to New England aimed for the middle ground between Sagadahoc and Cape Cod. This group, which formed the Massachusetts Bay Colony, struck near Boston, naming it after a village in the old country. Unlike the adventurers and separatists who preceded them, these Puritans were more typical of the contemporary English middle class, being better educated, involved in more skilled professions, and having come in greater numbers primarily to escape religious intolerance. Using maps made by Captain John Smith, they chose their landfall near Boston wisely, founding what has since become the economic and cultural center of New England.
The terrain near Boston was more yielding than that of Maine, yet firmer than that of Plymouth, which was located on the shore of Cape Cod Bay and had a greater abundance of shifting, sandy, droughty soils. This middle ground had wide, navigable, freshwater rivers; deep harbors; sheltered bays; and stable shorelines. Broad salt marshes were nurseries for fisheries and there were abundant freshwater springs. Soils were fertile and loamy, yet light enough to be grubbed free of roots and worked with handheld shovels and hoes; this was especially true in places previously cleared by the Woodland Indians for their crops of corn, beans, and gourds. Marsh hay-a mixture of reeds, sedge, and grass that grew naturally near high tide-was available for cattle fodder, which was essential for survival. Whitefish, alewives, lobsters, horseshoe crabs, kelp, and whatever else washed ashore could fertilize cereal grains, especially wheat and corn. The proximity to the sea moderated the bitter cold of winter, and lessened summer drought. The landscape was almost ideal. The climate, though seasonally cold, was healthful.
Within a century, the Massachusetts Bay Colony had become so successful that it expanded northward to engulf the failed colony of Sagadahoc, and southward to include Plymouth Plantation. The success of the Massachusetts Bay Colony was due largely to the industry of its inhabitants, who skillfully exploited the natural resources along New England's inner coast, but also to the natural affinity the English had for the land bordering the Massachusetts Bay Colony. Indeed, the English felt at home, naming their communities-Cambridge, Dartmouth, Ipswich, and Dorchester-after similar places on the other side of the Atlantic.
In fact, England and New England had similar landscapes and climates because both lands had a similar geologic history. Millions of years ago, in the Paleozoic era Old World and New World, motherland and daughterland were formed within the same mountain range near the center of the ancient continent Pangaea. Ever since then, they have been tied to the same geological fate.
To understand why the land of New England is so similar to that of Old England, and how the similar fieldstones on opposite sides of the Atlantic were created practically within the same foundry, it is necessary to go back to the inception of earthly time, 4.6 billion years ago. The story that follows explains why there are so many stones, why they are so widely distributed, and why they were perfectly shaped for human handling.
* * *
To the Puritans, hell was a place of eternal damnation, hot, dark, and sulfurous. However, in geologic terms, hell is not a place but a time. The Hadean Eon, spanning the first half billion years of Earth's history, was a protracted interval of volcanic fury that took place while the planet was still accumulating as a collection of fragments from asteroids and comets, and dust and gas from exploded planets.
During the Hadean Eon (an eon is a span of time long enough to hold eras and epochs), the heat released by intense asteroid bombardment combined with the heat released by radioactive decay to melt the planet. Molten lava oozed up to the surface, forming a bubbling ocean of red-hot liquid that quickly hardened into basalt, a black rock that formed Earth's most primitive crust. Meanwhile, heavier metallic components seeped downward, forming its core, a mass of iron that is solid metal at the center but liquid in the outer core. Earth's rotation (spinning more rapidly than now) caused swirling motions within the outer core, which produced the planet's magnetic field, and thus protected the early Earth from the sun's intense ionizing radiation.
Between the Earth's core and its crust lies its mantle, an enormous region of warm, dense, dark-greenish rock that is solid, but malleable enough to flow and be stretched. The continents are made of the lightest of Earth's solid layers. From its hot, molten origin, Earth became a solid but squishy glob of soft rock that rotated rapidly on its tilted axis, perhaps up to five hundred days per year, while wobbling like a top.
As Earth's interior melted, volatile gases boiled up and created an atmosphere rich in noxious substances. Nitrogen, carbon dioxide, and water vapor were heavy enough to be retained by Earth's gravity, whereas lighter gases such as helium were mostly lost to space. When the atmosphere first formed, Earth's crust was as hot as a broiler, prohibiting the condensation of the water at or near its surface. Any drops that fell to the surface quickly flashed to a cloud of steam, then back to vapor. Therefore, all the Earth's water was held in high clouds so dense and thick that they blocked out the sunlight completely.
At that point, Earth's lava surface was perpetually dark and parching hot. What dim light there was came from the orange-hot glow of flowing lava; the constant "heat" lightning from distant clouds; and the yellow-green flashes of meteorites, which until about 3.8 billion years ago streaked through Earth's carbon-rich sky by the billions.
Eventually, the Earth cooled down. The shroud of vapor condensed into mist, then mist to droplets, and droplets became drops. Rain began to fall, not just for a few hours or a few days, but for thousands of years, until the original atmosphere had rained itself dry. Torrents of water drenched the now solidified lava that covered the entire planet. Rivulets of fresh water-not yet stained by salts, clays, and dissolved organic compounds-flowed noisily in the darkness, seeking the low places. First, pools were formed, then ponds, lakes, and finally a global ocean. Simultaneously, the sky gradually brightened, as though part of a long, drawn-out dawn, thousands of years in the making. One day, the first gleaming ray of sunlight broke through the thinning clouds to strike an azure ocean so young that it was not yet salty, and so expansive that hardly any dry land existed.
As the Earth cooled further, lingering volcanism produced masses of molten rock called magma that were lighter in weight, lighter in color, and richer in silica than Earth's earlier, heavier, more primitive magmas that produced only basalt. These lighter-weight masses of molten rock cooled to make lighter-colored rocks similar to granite, which floated slightly higher above the mantle than their basaltic counterparts. Over time, blotches of granite crust coalesced like flotsam on a stream, fusing into proto-continents that were light enough to float above the level of the sea, thus making dry land.
At some point in Earth's cooling history, the outermost fifty miles or so-equivalent to the thickness of the skin on a peach-became a rigid shell called the lithosphere. Because the lithosphere lay above a much thicker, softer, still-swirling mantle, it broke up into giant tectonic plates, which glided slowly over the surface, carrying the continents along for the ride. No longer a hot, dark, crater-blemished, quiet lump of debris gathered by gravity from the solar system, Earth had been transformed into a machine, powered by the heat from its interior, radiation from the sun, and the angular momentum of its planetary spin. The tectonic plates moved independently, like juggernauts, making mountains where they collided, ocean basins where they separated, and enormous valleys where they slid against one another.
Earth's atmosphere traveled quickly over the oceans, producing wind and waves, and the ocean's sluggish movement over its crust produced tides and currents. Wind storms, thunder, waves, torrents of running water, earthquakes, and volcanic explosions were the sounds of Earth's vital fluids moving about, yet there wasn't a single creature alive to hear them.
Life began about four billion years ago, probably on some hot, briny, pitch-black, undersea volcanic vent. From that remote bacterial beginning, the evolution of life commenced. For most of Earth history, however, life would remain simple and confined beneath the sea. Only after ninety percent of Earth history had passed would creatures evolve legs and become strong enough to live on land. It was during this life transition-from oceanic slime to terrestrial animals-that the raw material for the stones of New England began to form.
This inception took place in the Iapetos Ocean, the precursor to the Atlantic, which occupied roughly the same place; Iapetos was the mythological father of Atlas, for whom the Atlantic is named. The Iapetos Ocean disappeared as the ancient landmasses of Africa, Europe, and North America converged upon each other during the formation of Pangaea. The former ocean's water could easily flow elsewhere on Earth. But the solid material that had lain between the three continents-abyssal marine mud, plankton oozes, volcanic islands, old shorelines, limy reefs, small blocks of crust, and other earthly flotsam-was scraped off the floor of the ocean and added to the edge of North America, which at that time lay much farther south, near the equator.
The culmination of this continent-to-continent collision occurred about three hundred million years ago, shortly before the dinosaurs began to rule the planet. Called the Acadian Orogeny in New England and the Caledonian Orogeny in Britain, it produced a mountain range that traced a seam through the center of Pangaea, where the continents had been stitched together. Indeed, the fjord-torn mountains of Norway shared the same bedrock with Greenland; the central Appalachians were attached to West Africa. The lands in between-New England, maritime Canada, and Britain-were pressed tightly together during the three-way collision.
A small fragment of continental crust geologists call Avalonia, caught up in this collision, has since broken into separate pieces. One now lies beneath southeastern England, another beneath southeastern New England. On the other side of the collision lay what is called the Greenville Terrane, which later broke up as well; its rocks form the northwestern part of the British Isles, including Scotland, and the northwestern edge of New England from western Connecticut to western Maine. Most of what lies between-Ireland, central England, and Wales on one side of the Atlantic and most of central New England on the other-was made from the mud and clay of the Iapetos Ocean.
Any land caught in the collision zone and squeezed horizontally by the relentless tectonic stresses was also thrust vertically upward, producing a mountain range so massive that it couldn't be supported by the strength of the Earth's crust alone. Hence, the vast bulk of the mountain range, extending from Florida to northern Norway, sank deeply into the softer mantle of the Earth, in places as much as twenty miles. Essentially, only the upper part of the mountain chain remained above the ocean while most of it lay well below sea level, as though it were an enormous stone iceberg. (Something similar is happening in the Himalayas today, where the ongoing collision between India and Asia has produced a range of mountains made by materials scraped off the floor of a disappeared ocean. The Himalayas above sea level today are but a small fraction of their total mass underground.)
It was in the root of the "Acadian Mountains" whose eroded stubs are now the northern Appalachians, that New England's stones were created ten to twenty miles straight down. A dry, hot mélange of minerals baked slowly within the Earth, at a depth more than five times that of the deepest mine. Temperatures sometimes exceeded that of flowing lava. Pressures were thousands of times greater than those above ground. Briny waters were forced out of pore spaces as they squeezed shut, carrying with them gold, silver, mercury, and other precious metals dissolved in boiling fluids. Carbon, nitrogen, hydrogen, and other lighter, volatile elements that had originally been extracted from the Earth's atmosphere by biological processes and sunk to the ocean floor burned away and were vented back to the skies. Primary rock-forming elements-silicon, oxygen, aluminum, calcium, sodium, iron, potassium, magnesium-were left behind and forced to recombine into new minerals that were stable under these new conditions. Clay cooked to mica, grit into quartz. Enormous masses of rock the size of Rhode Island and rendered soft by the heat stretched and bent like taffy, folding into each other, miles below the surface.
Over time, the once mundane materials of the former Iapetos Ocean-mud, muddy sand, sandy mud, sand-were transformed into the beautiful banded rocks visible over most of New England today. Some of these rocks are layered like a cake. Others resemble succotash, with clots of crystals. Some of the manufactured minerals would become vital to early Yankee industry-pink feldspar for ceramics, smoky quartz for glass, brown garnets for abrasives, white barite for paint thickener, bronze sheets of mica for furnace windows, green talc for lubricants, gray veins of graphite for pencil lead, and black specks of iron oxide for steel. Colonial mining was a colorful, and locally successful, business.
* * *
Pangaea was destined to fall apart. The thickened crust acted like a skullcap, trapping the heat that is always escaping from the Earth's interior. As the upper mantle warmed beneath Pangaea, it expanded slightly, lifting the supercontinent upward and producing a bulge more than a mile high. The continent stretched, thinned, and finally broke, similar to the way the top of a loaf of bread sometimes splits. The uplift and rupture of Pangaea formed a volcanic rift zone that ran from south to north, from Georgia to Greenland.
Along the crest of the rift zone were long basins (similar to those of California's Death Valley, Jordan's Dead Sea, and Africa's Lake Victoria), each of which subsided as the crust pulled apart. Initially, this occurred slowly enough for the rivers draining from the highlands to be able to keep the widening basins filled with sediment, crossing them with broad, meandering channels. But eventually the subsidence along bordering faults was so rapid that deep, narrow lakes were created. Sediment being shed from the eroding highlands poured into these lakes. On several occasions, the rift fractures penetrated so deeply that they tapped into pools of basaltic magma, which gushed upward along fissures to form lava lakes up to several hundred feet deep and tens of miles long. Such lava flows, after solidifying and being tipped to the side, later became known as traprock ridges.
Excerpted from Stone by Stone by ROBERT M. THORSON Copyright © 2002 by Robert M. Thorson
Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
|1.||England and New England, Common Ground||11|
|2.||Making the Stone||29|
|3.||Burying the Stone||55|
|4.||Taking the Forest||75|
|9.||Back to Nature||205|
|10.||Writ in Stone||220|
Posted April 25, 2011
No text was provided for this review.