We see the phenomenon exhibit itself over and over as we rumble northward across the land—we see it through central Gloucestershire and Warwickshire, through Rutland and Leicestershire, across Nottingham and Lincolnshire—so that when, a day or two after I had left the warmth of Dorset, I found myself in the cold of Lincolnshire coasting along the A15 northbound from Lincoln (where there stands a fine Jurassic cathedral, made of just the same-age limestone as that at Wells, down at the far southern end of the outcrop) to Scunthorpe, almost exactly the same held true. To my right rose high limestone plains, buffeted by North Sea winds, dotted with sheep, flat enough and suitably exposed for the building of great Royal Air Force runways, training schools, and hangars. To my left, all was unsubtly different: A yellow cliff fell steeply away, and below it, spread almost flat like an unfolded survey map, lay a long, low valley, thick with farms, populated and cozy. The Middle Jurassic formed the upland landscape to my right; the Lower Jurassic the lowlands to my left.
Seen today, this pikestaff-plain exposition of how the rocks below make the hills above has the standing of a classic of English geology. Not a single guidebook to the geology of England fails to provide an illustration of the great hills at Crickley or Snowshill or the scarp face above the ancient wool town of Wootton-under-Edge. And, knowing now what William Smith had realized, explained, and then colored onto his great map when he saw this vast extent of hillside two centuries ago, “It all seems far too easy!” I find myself tempted to exclaim, as Thomas Huxley cried out on first reading Darwin: “How very stupid not to have thought of that before!” That William Smith was first to do so was a measure of the man’s extraordinary achievement: to see what others could have seen but never did, to set down on paper what others might have suspected but never felt confident enough to declare.
The rock type that appears most consistently across the hundreds of miles of the Middle Jurassic outcrop is invariably an oolitic limestone. The term comes from the tiny, fish-egg-like concretions of which the limestone is made—and which, in some of the coarser-grained oolites, can easily be seen with the naked eye. Under the microscope the individual ooliths look like pearls, or mother-of-pearl accretions, or those many-layered gobstoppers English schoolboys once knew so well*—and yet in place of the crystal of aniseed at the heart, there is in the case of the Cotswold ooliths a tiny piece of quartz, or a fragment of shell. Layer upon layer of calcium carbonate had been deposited around this nucleus: Centuries of rubbing and jostling in Bahamas-warm blue seas then kept the slow-forming ooliths small and smoothly spherical; and their color, freshly formed, has invariably either been carbonate white, or else, if there happened to have been more than the usual complement of dissolved iron in the waters of the time, reddish brown.
But hundreds of years of gentle weathering have changed all of England’s Jurassic oolites into the masons’ most magical building stone. The physical nature of the rocks alone has long rendered them a sculptor’s dream. Their bedding planes are straight and well defined, and either the chunks of quarried rock divide naturally into huge freestones, durable and massive and ideal for making big, strong, impressive buildings, or else can be sawed into flat sheets of ashlar, which can be bonded to rougher rocks and give, less expensively, the same harmony and integrity of look and color. Once in a while relics of the old coral reefs are to be found—for Jurassic waters were blue and shallow, much like the Caribbean waters of today—and make for good building stone too: But they are knobby and ragged, the quarrymen call them hardstone, and most locals think of them as less pretty than the oolites themselves.
This “Cotswold stone” has a well-deserved worldwide reputation: The stones are solid, easy to work, more than amenable to simple carving, perfect for bearing large loads. Above all else, though, the Cotswold stone is quite simply beautiful. The humblest of workmen’s cottages, if fashioned from a Cotswold oolite, is a lovely thing to see—and a huddle of the warm-looking Jurassic stone houses, clustered amicably in some river-carved notch in the meadows, can be so lustrously perfect, so quintessentially English that seeing it brings a catch to the throat.
In the villages that did well enough from the wool trade to evolve into something more than a simple confection of pretty houses, oolite stone was used to make just about everything—the columns, quoins, and mullions of the marketplace, the walls and facings of the cottages, the manor house steps and dove-cotes, the fonts, the choir stalls, the bell towers and the transept floors of the parish church. In one Cotswold town, Bradford-on-Avon, there is a stone bridge with a stone jailhouse at its center point—durable, indestructible, and prisoner-proof.
The walls between fields, too, are built dry-stone, of oolite—and the contrast between a countryside that is apportioned by hedges and its neighbor with its fields divided by walls can be blisteringly sudden: In Lincolnshire, where the escarpment of the Lincoln Edge thrusts up with an immediacy reflecting the narrowness of the outcrop there, hedge becomes wall in just a matter of yards. Glance down from the edge, and every field is surrounded by blackthorn, hornbeam, and dog rose; glance up, and the fields are broken up by long stands of rough and mottled stone, tough, enduring and very, very old.
And yet it is the weathering, more than the simple durability, that provides the magic of the Cotswold oolites. The pale-honey coloration of newly cut stone, the rich orange and creamy reds of older, well-weathered buildings are quite sublime: The rock has given entire villages—Bourton-on-the-Water, Stow-on-the-Wold, Cirencester, Chipping Norton—an architectural wholeness; and it is a fine piece of irony that the poorer old homes, made of lesser-quality stone, have weathered in far more interesting ways than have the great houses built of the finest, unblemished freestone blocks. The patchiness of the weathered yeoman stone seems to give an extra dash of character, an additional element of charm.
The Middle Jurassic Great Oolite has given a distinctive look to entire cities too, a look that is now a part of the essence, the quiddity, of their very being. How would the crescents and circuses and terraces of Bath look if they had been constructed of some lesser stone? How much less lovely would Oxford be if the oolitic freestones of so many colleges and noble buildings had not been available, and the structures had been fashioned instead from a dour and ancient granite like the stones of Aberdeen, or from a grayish Millstone Grit of the North, of Silurian shales and gray slates from Bethesda, or made from a dull red sandstone like that found in unexceptional Middle English cities like Northampton, Doncaster, and Carlisle? The Middle Jurassic limestones make for a building stone of such gentle loveliness that its Cotswold walls, as J. B. Priestley wrote, know “the trick of keeping the lost sunlight of centuries glimmering upon them.”
There is a little more complexity to the oolite than merely to say that the Middle Jurassic—even the outcrop between Bath and Lincolnshire—is composed entirely of it. There are, as William Smith himself found and described early in his career, at least two types of oolitic limestone represented in the epoch—an Inferior Oolite at the base of Middle Jurassic and a Great Oolite at the top of it. Between the two lies a layer some hundreds of feet thick of a distinctive claylike rock that, since it had the useful quality when mixed with water of fulling, or leaching the greasy lanolin from lambswool, was (as already noted) called Fuller’s Earth.*
Within the oolitic horizons there are countless variations—of color (gray to buff, orange to ochre to pale scarlet) and fineness of texture, size of oolith, and width of banding and bedding plane. I chanced during my journey upon a roadside quarry near the village of Northleach, and the ebullient owner happily showed me around, pointing out with delighted pride the different colors and thicknesses of his rocks, and the uses he could make of the various types.
He used to be a farmer, but he had given it up back in the 1990s when he decided there was more money and amusement to be had from working the land below than trying to make ends meet from the land above. He had become a canny businessman: Build the Future, was his slogan. Use Natur
al Stone. He had handsome brochures, tempting customers with warnings—such as the charming thought that lichens would grow on untreated stones, that fragments of shell might protrude from walls and mantles, and that the presence of something called quarry sap might make the more delicate pieces crack in times of severe frost, and advising they be protected with hessian or burlap sacking.
He sold oolite by the ton for houses and walls; he also had a small gang of resident masons who slaved away in dusty warehouses making lintels and fireplaces, finials and corbels, carving gravestones and coats of arms. An admirer of English stone, currently living in Saudi Arabia, had recently ordered a globe, three feet in diameter: It would take the quarry owner’s chief mason three days to finish it, so long as his excavator could delve deep enough among the freestone blocks to find a chunk big enough and free enough of faults to allow for the extraction of a one-ton sphere.
What his quarry did not sell, though, was the one lithological expression of the Middle Jurassic that is too rare to market anymore, and that is what the quarrymen used to call “the pendle”—the so-called oolite “slate” of the Oxfordshire village of Stonesfield (not more than a couple of miles from Churchill, where William Smith was born). The rock is not a slate at all, but simply a very thin-bedded version of the usual limestone, and which has for centuries been used to finish the roofs of Cotswold houses. A truly classic manor house, that one might find between Oxford and Bath, should have its walls made of Jurassic freestone or faced with oolite ashlar, and its roof made of overlapping shingles of Stonesfield slate.*
The quarry sap mentioned in the Northleach brochure plays a vital part in the making of Stonesfield slate—which, not being a proper slate, cannot be manually split along its bedding planes. Quarrymen would only remove the pendle—they had to mine for this rock, using shafts and burrowing along narrow horizontal tunnels—between October and Christmas, and then leave the rocks set in clamps until the onset of the first sharp frost. The moment that this frost came—invariably in the middle of some January night, and the church bells would have to be rung to summon everyone—the miners would dash out to their waiting clamps of pendle and see if the iced-up quarry sap had done its work, shattering the limestone into tile-thin slabs.
If it had, then the men spent the summer cutting and shaping the slates—120,000 of them in one Victorian summer at the Kineton Thorns pit alone. But if it had not, then the uncracked slabs of pendle would have to be buried in the cold earth to preserve their sap—for if this quarry water was allowed to leach out it could never return, the rock could never be split, the slates would go unmade, and the men would go unpaid. It was a harsh and unforgiving business. Few are the industries that require frost to keep them in business: The villages of Stonesfield and Collyweston, unique in the land, came to rely for centuries on the regular onset of bitter cold, just as a Punjabi farmer would rely, year after year, on the coming of the monsoon.
The quarrymen would have another source of income, though. Fossils were to be found in huge abundance in the Stonesfield slate—and not just mollusks and belemnites, the standard fare of the collector and the academic. Here there were pterodactyls, dinosaurs, crocodiles, fish, cirripedes, annelids, starfish, and plants. Each time a quarryman or a slater might find a spectacular occupant he would pry it carefully from its limestone resting place and prop it tantalizingly in his cottage window. Geologists from Oxford University, on the hunt for specimens for teaching or research, would know to pass by Stonesfield each weekend, and scores of guineas would change hands for some of the choicer finds.
After a pleasing week of wandering along the southern and eastern Midland outcrops of the oolites (and which were invariably garishly covered with the bright yellow flowers of Brassica napus, oilseed rape, which flourishes noticeably well on the limestones, with their six inches of highly alkaline topsoil), it was time to cross the Humber, and then watch the Middle Jurassic very nearly vanish. For some while, once I had arrived at Lincoln (where I bought for thirty pounds [about forty-five dollars] a nice varnished specimen of the Liassic ammonite Asteroceras) I had been aware of the looming presence to the east of the uplands of the Cretaceous chalk—which William Smith had recognized from forty miles away, that day in 1794 when he climbed up the tower of York Minster. Now the chalk pressed closer and closer, until, just outside the Yorkshire village of Market Weighton it lay not—as it should—on an Upper Jurassic horizon, like Portland Stone or Purbeck Beds, but on the Liassic rocks of the Lower Jurassic. At Market Weighton there were no Middle Jurassic outcrops at all: Northward up to the village of Thixendale the chalk lay directly either on the Lias or, for a very few miles, directly on top of the Permian.
A classic Lias ammonite, Asteroceras.
An entire geological epoch was missing—and for no more complicated reason than that during Middle Jurassic times there was a lozenge-shaped axis of uplifted high ground to the north of Market Weighton, where no waters could lap and inundate, and where no rocks, limestones, shales, cyclothems, or marl-stones could ever possibly accumulate. For half an hour I drove north through a series of villages that had never known the Middle Jurassic, knew nothing of oolites, had few fields of oilseed rape and that seem to have been held economic hostage to their geology after being surrounded on the one side by chalk and on the other by clay. The village houses were uniformly ugly and built of brick; the fields were divided, if at all, only by straggling and ill-kempt bushes. I felt strangely prejudiced against the place; and Smith’s diaries showed he hurried through the countryside here too, eager to get back to a part of English geology for which he felt a keen affection but which here had found no place to settle.
North of Acklam, Leavening, and Burythorpe it returns once more, however—though this time in very different form. Just as with the looming presence of Yorkshire’s chalk wolds to the east, so now another clump of hills began to rear darkly in front. These were the North Yorkshire Moors, heather-covered and wild, incised by deep valleys, and topped by vast flat acreages of unspoiled parkland.*
But the rocks here are not oolitic limestones—because the seas here were neither shallow nor Hockney blue. This was the delta of an immense river that coursed down from the North Sea Dome much as the Rhine courses out from Germany near Rotterdam. The rocks are thick—the river must have been Yangtze vast and sent billions of tons of sediment into the sea each of the five million years of its existence—but they are not limestones: They are sandstones and thick shales and, near Cleveland, ironstones. There are few marine fossils here, but a huge number of specimens of trees and fossil plants—horsetails, gingkos, cycads—and even on the Yorkshire coast, very thin bands of coal. This is the Middle Jurassic still: But as one can tell from the purple billows of heather and the cold and lonely roads snaking past secret radar stations and to the cliffs of the North Sea, it is made up of rocks very different from those at the other end of the country.
William Smith saw all of this countryside in the first two decades of the nineteenth century—he saw and traveled across and mapped all this and a great deal more besides. When I followed my own route two hundred years later I did so by dint of using a series of government-issued geological maps—most of them at a scale of ten miles to the inch, some at one mile to the inch, depending on where I was, where I wanted to be, and how much detail I needed to know. And in using those maps I would realize, each day that I pulled them from the glove compartment, spread them out before me, and marveled at their accuracy and real beauty, that William Smith had, in essence, created them. He had been the first; it was his labors and his ideas that stood behind the artful confections that now guided me, and that guide a million others today.
There is something of a fine irony in the fact that my journey finished where it did, in this remote and enchanting part of North Yorkshire. For in the 1820s William Smith lived and worked here too, mapping and surveying an outcrop of the Middle Jurassic sandstones about five miles inland from the coast, at a village called Hackness. It was at Ha
ckness that the fortunes that had eluded him for so many long and wretched years finally caught up with him, his life began to turn around, and he could begin afresh.
Now, however, with the Jurassic of the Dorset coast hundreds of miles behind, and with the Jurassic of Yorkshire before me slipping off the cliffs into the cold North Sea, is the moment to pick up the narrative again. To do so it is necessary to wind back the clock and return to 1802—to the year when William Smith, still young and energetic and with his later ill fortunes both unanticipated and a very long way off, embarked on what would become the most creative period of his life.
12
The Map That Changed the World
Clydoniceras discus
It was a work of genius, and at the same time a lonely and potentially soul-destroying project. It was the work of one man, with one idea, bent on the all-encompassing mission of making a geological map of England and Wales. It was unimaginably difficult, physically as well as intellectually. It required tens of thousands of miles of solitary travel, the close study of more than fifty thousand square miles of territory that extended from the tip of Devon to the borders of Scotland, from the Welsh Marches to the coast of Kent.
The task required patience, stoicism, the hide of an elephant, the strength of a thousand, and the stamina of an ox. It required a certain kind of vision, an uncanny ability to imagine a world possessed of an additional fourth dimension, a dimension that lurked beneath the purely visible surface phenomena of the length, breadth, and height of the countryside, and, because it had never been seen, was ignored by all customary cartography. To see such a hidden dimension, to imagine and extrapolate it from the little evidence that could be found, required almost a magician’s mind—as geologists who are good at this sort of thing know only too well today.