Making Sense of the World

William Smith is a familiar name to generations of geology students. His geological map of England, Wales and part of Scotland, published in 1815, was an astonishing achievement that earned him recognition as one of the founders of modern geology. Mt. Everest is another familiar name, but George Everest, for whom the mountain is named, and William Lambton, his predecessor as superintendent of the Great Trigonometric Survey of India, are known to few. The imbalance is a pity because the 40-year-long survey was an extraordinary feat, and the scientific result has been just as insightful as that from Smith’s work.

Smith’s story is engagingly recounted by Simon Winchester, whose “The Professor and the Madman� captivated readers with its story of the creation of the Oxford English Dictionary. When Smith was active in the late 18th and early 19th centuries, scientific debate about the Earth was very active. The intellectual center was Edinburgh, Scotland, and the intellectual leader was James Hutton, a wealthy and well-educated Scot who was fascinated by the geology he saw around him. Hutton’s great treatise of 1795, “Theory of the Earth, With Proofs and Illustrations,� is today considered to be the cornerstone on which the edifice of modern geology has been built. One of Hutton’s challenges to ideas of the day was a direct assault on the biblical interpretation of Earth’s history. In the evidence of rocks there seemed to be, Hutton wrote, “no vestige of a beginning, no prospect of an end.� The rock record was one of uplift, erosion, transport of the debris of erosion by streams, deposition in the sea, formation of new layers of rock, uplift, erosion and so on, unending.

Smith’s work reinforced and expanded Hutton’s ideas. A blacksmith’s son from Oxfordshire, Smith joyously collected fossils of sea urchins and other marine life on his uncle’s dairy farm, and his joy eventually grew into an obsession that had a major effect on the way we view the world. Largely self-educated, Smith was apprenticed to a surveyor as a young man and soon moved from determining field boundaries to the more exciting task of laying out routes for canals. His passion for fossils provided a very practical bonus. Smith discovered that the rocks of southern England were layered--�stratified� is the geological term--and that each layer or stratum contained a unique assemblage of fossils. Knowing that some strata were porous and caused canals to leak, Smith could avoid the bad spots and lay out practical routes from his knowledge of fossils. From canals he progressed to coal mines and then to the design of drainage systems, and his work took him all over England.

Eventually, he decided to use his information to prepare a countrywide map showing where the various strata reached the surface. Traveling almost continuously as a consultant, Smith made personal observations that provided all the data from which he compiled the first geological map of England and Wales. Published in 1815, the map is a thing of beauty. The cost bankrupted Smith, throwing him into debtor’s prison, ruining his family life and exposing his work to plagiarism. Fortunately, near the end of his life, his fortunes recovered and honors flowed his way as the scientific establishment came to realize what he had done.

Smith had prepared a map unlike any other, a map of the underside of an entire country, a map with soils, vegetation and other surface features stripped away to show the distribution of the rocks of which England and Wales are made. The sequence of strata and the evidence that uplift and erosion had at times removed some of the strata were recorded. Also recorded was evidence that again and again, whole communities of sea creatures had lived, become extinct and been replaced by new creatures. Hutton’s writings were complex and his message difficult to comprehend. Smith’s map was clear, straightforward and accessible to all.

Although their professional lives overlapped, Smith probably did not meet Hutton, nor is it clear that Smith read Hutton’s great work, but with Smith’s map of the strata, a new generation of geologists realized how Hutton’s work could be tested and expanded. It was soon demonstrated that the fossil-bearing strata in England could be matched with those across the channel in France--that is, it was possible to correlate strata from one country to another; a gap in the pile of strata in one location could be filled by data from that stratum elsewhere. By comparison and correlation, strata all around the world could eventually be sorted into a relative order of ages. In any pile of strata, the oldest will be at the bottom, and one of the challenges raised by the great map was to find the oldest. That search is still proceeding; the most ancient rocks discovered on the Earth so far--in Canada--are 4 billion years old, but other lines of evidence indicate the Earth is at least 4.56 billion years old, so still older rocks may one day be found. The title of Winchester’s book is something of an overstatement; Smith’s map did not change the world, but it played a major role in our understanding of the world and its long history.

The same is true of the Great Trigonometric Survey of India, which set out to measure the curvature of the Earth. The survey was the brainchild of William Lambton, a quiet, likable genius who was fascinated by geodesy, the science of the precise measurement of the shape of the Earth. Lambton started his career in North America as an ensign in the 33rd Foot of the British army. Taken prisoner at Yorktown at the end of the American Revolution and eventually released, he was sent to New Brunswick where, for 12 years, he surveyed land holdings, participated in the delineation of the boundary between the United States and Canada and spent his spare time reading mathematical tracts on geodesy.

When Lambton was promoted in 1796 and ordered to India by his commander, Arthur Wellesley, later Duke of Wellington, his opportunity had arrived. As John Keay’s “The Grand Arc� describes in fascinating detail, Lambton proposed, and Wellesley supported, a geodetic survey to be conducted along the parallel of longitude that roughly bisects India. The practical side of the venture would be a network of trigonometric points by which the mapping and development of India could proceed. Lambton’s personal goal, however, was a scientific one--the measurement of the shape of the curved surface of the Earth. It had been established early in the 18th century that the Earth’s shape approximates an ellipsoid of rotation, being flattened at the poles and bulging at the equator. The exact amount of bulging and whether the distortion from a sphere was regular or irregular remained in doubt. Lambton’s goal was to remove those doubts.

Keay is an expert on the history of British India and has published extensively. His account of Lambton’s great survey is gripping, but even more gripping is his account of the work of George Everest, the argumentative martinet who succeeded to leadership of the survey following Lambton’s death in the field in 1823. Carrying the survey steadily northward through jungles and swamps and eventually to the Himalayas, wracked by tropical diseases but ever vigilant to avoid even the tiniest error of measurement, Everest completed Lambton’s visionary task, received the accolades of the scientific community, was knighted by Queen Victoria and had the world’s highest peak named in his honor.

Near the end of the Great Trigonometric Survey, Everest discovered a discrepancy between the astronomically determined distance between two stations 370 miles apart and a measurement made by triangulation. The triangulation measurement was 5 seconds of arc (about 500 feet) greater than the distance between the stations calculated from astronomical determinations of the latitudes and longitudes. Keay does not enlarge on the point even though that discrepancy led to a very important scientific discovery. Everest wondered if the problem lay in the use of the surveyor’s plumb bob--the weight suspended below a theodolite. A surveyor uses a plumb bob, which is simply a small mass of metal (the bob) hung from a string, to determine the vertical (the plumb line). Everest suspected that the gravitational attraction of a large mountain mass might pull a plumb bob ever so slightly off vertical and thus introduce a measurement error. He asked John Pratt, archdeacon of Calcutta and a skilled mathematician, to calculate the expected deflection and look for its effect in the survey data. Pratt made the practical assumption that the Earth’s crust was a layer of constant thickness and that mountains simply sat on top of the rigid layer. His calculations showed that the Himalayas should indeed cause a detectable deflection of the plumb bob, but the observed errors in the survey results were less than those calculated--it seemed, in effect, as if part of the Himalayas were missing.

Pratt considered the problem further and discovered that, for survey stations close to the ocean, the deflection of the plumb bob was actually toward the sea rather than away from it. Water is less dense than rock and its gravitational attraction of the plumb bob would be less than that of rock. Pratt concluded that beneath the rocks of the oceanic sea floor must be much denser rock than rock on the continent--water, in effect, played little or no role. Pratt extended his ideas further and suggested that all the survey results could be explained if the Earth consisted of blocks of rock of different densities.

When Pratt published his results in 1855, George Airy, the astronomer royal, suggested that the discrepancy could be better explained if the Earth’s crust were of essentially constant density, that it was underlain at some depth by a layer in which some kind of dense rock was so hot it was plastic and acted like a viscous liquid. High spots like the Himalayas, he argued, were underlain by roots that projected into the plastic layer. In effect, Airy suggested that mountains were like icebergs and that the crust of the Earth floated on a denser substrate.

Airy’s hypothesis was the key step in solving a puzzling problem that had worried people for a long time--how to account for the Earth’s topography. If the crust floated, it was much easier to understand why every geologist had come to accept, as G.K. Gilbert said in his presidential address to the Geological Society of America in 1892, that “the geologic history of every district of the land includes alternate submergence and emergence from the sea.� Hutton saw the problem, Smith mapped the evidence, and now here was an explanation for how the crust could slowly bob up and down.

American geologist Clarence Dutton named the flotational condition of the crust “isostasy,� a word meaning “equal standing.� Isostasy is a key property of the Earth. Indeed Dutton argued that it could be geology’s core or unifying theme. But one further step remained. Isostasy explains vertical movement of the crust, but it does not explain lateral, or sideways, movement. That final piece is “plate tectonics,� a process by which entire fragments of the Earth’s outermost rocky layer slide around on the hot, deep, plastic layer below. Plate tectonics is isostasy on a grand scale, and what a story there is still waiting to be told about the struggle to realize the plate tectonic revolution.

Thanks to Everest’s discovery of the discrepancy, and to Pratt’s pursuit of its cause, geologists have a vastly better understanding of the way the Earth works. In “The Map That Changed the World� and “The Grand Arc� Winchester and Keay have chronicled three remarkable figures and a time when the scientific study of the Earth was moving rapidly ahead. Smith, Lambton and Everest are all important, and their lives--as the authors skillfully show--make fascinating reading.