The Map That Changed the World (10 page)

The chain-rope was clattering him slowly downward, and toward an important moment—for as he continued to gaze at the slowly passing walls, so everything around him on the sides of the mineshaft abruptly changed. Within a matter of inches the nature of the rocks—their look and feel and color and hardness—was all altered.

Where there had been these limey, shaly, reddish-greenish marly limestone rocks above, now instead on the sides of the shaft was a facies of thick, sandy, grayish brown rocks that appeared wholly and profoundly different.

Moreover, if he looked closely at the gradation between one type and the other, Smith could see that this change did not even occur within a matter of inches—it was much less, so much less that in fact there was a verifiable point at which the change occurred, a line above which was one rock, the Red Marl, and below which another, the Grey Sandstone, without any gradation between them that was worthy of the name.

And it wasn’t just the nature of the rocks, their lithology. Just as noticeably the
attitudes
of these new rocks had changed too: Where the Red Marls had sloped neatly at a gentle angle, all pointing in one direction, these new gray-brown sandstones—ugly and rather unappealingly harsh rocks, as they appeared to Smith in his guttering candlelight—appeared to plunge deeply downward. Their bedding planes, the cracks that separated one bed of sandstones from another, were steeply inclined, and in places they were very evidently folded, and in places so folded they had been shattered and broken up by dozens of small dislocations, as though the bands of rock had once been contorted by a giant vise, all twisted, flattened, and cracked, and then released and left to lie tumbled and in disarray.

It was all so very strange. Back up at the top of the shaft, near the lip, had been these beguiling, neatly laid-out sheets of almost horizontal strata, with just their faint slope in the vague direction of London. Now, below them, the rocks were contorted and thrust in all manner of different directions, most of them dipping
down toward the center of the earth. As mentioned in the previous chapter, modern structural geologists using radiometric dating techniques, taking deep-drill cores, and performing seismic examinations have recently established that Somerset’s coal measures were folded and twisted by the great Variscan mountain-building period that occurred 290 million years ago, when the African and European tectonic plates collided. But none of this was known or even vaguely conceived by Smith or by any geologist then alive. So Smith could only stare at the junction between the rocks and wonder—Why? How? How could one possibly make sense of such a bizarre arrangement?

B
y chance this was exactly the time when the stripling science of geology was indeed trying to make sense of such structural oddities. James Hutton, the gently born Scots doctor who was one of the leading philosophers of the age, was at the time of Smith’s work just three years away from publishing his seminally important three-volume book
The Theory of the Earth
, which sought to explain countless facts about the earth—including precisely how such an internal discordance among strata, a so-called unconformity, had first come about.

It was a very similar unconformity, in fact, that had first set Hutton thinking. He had seen another arrangement of rocks, much like those Smith was seeing at High Littleton, in a rocky cliff on the North Sea coast of Scotland, at a now-hallowed site called Siccar Point in Berwickshire. There, thick layers of the Old Red Sandstone of Devonian times were—and still are, of course (though now much chipped by the geological hammers of ten thousand students)—lying flat on top of steeply inclined hard gray sandstones of the Silurian period. Hutton suggested that both of these sets of rocks must have been laid down by deposition from a sea, and that the gray sandstones, after being laid down, had been lifted up and out of the sea by great and mysterious crustal processes, had been subjected to all manner of con
tortion and twisting and deformation, then eroded so that the top of all these twisted rocks was cut off and smoothed and flattened, and finally submerged again by the sea in Devonian times to allow red sandstones—what would eventually be called the Old Red Sandstone—to be laid down on top.

And the important ideas that Hutton grasped from pondering this, and which he declared in the final volume of the great book, were these: first, that the processes of formation of rocks are the same processes—creation, erosion, deposition, change, and erosion—that we see today, whether in a stream bed, by the sea, or on the flanks of a volcano; second, that the earth works today more or less as it always has; and third, that these processes, tiny and unimportant though they may seem in the short term, take place over unimaginably long periods of time, over an uncountably large number of years, so that anything that is observable in the rocks around us today can be imagined as having happened as a result of normal, everyday occurrences taking place over aeons of geological time. “The present,” said Hutton most memorably, “is the key to the past.”

If one could imagine this, wrote Hutton—and he wrote these words at almost the same time as Smith was clambering down into the Somerset mines—then one could think of the earth as having “no vestige of a beginning and no prospect of an end.” It was a staggering thought, quite appalling to some—but it was the kind of thought that was to permeate the world of geology into which Smith-the-surveyor was just now making his entrance.
*

I
t was in and among the gray sandstones that the true wealth of the Mearns collieries, and all the neighboring mines, was held. For these were coal measures, and in them, as Smith was to see as the mine chain clanked him lower still, were—thin, distorted, and plunging deep below—the precious veins of coal.

The miners, tough and taciturn men, had given names to all the seams, as miners all around the world always do. Coal seams may all look the same, much as all coal may look alike; but in fact all seams as are different as all people, when they are looked at as closely as a miner has to look. Each band has an internal pattern, a collection of fossil types, an appearance, a feel, a
personality
, that makes it instantly recognizable. A miner will be lowered down the shaft and step out into the blackness and know in an instant where he is, how deep in a series, how far down within a seam.

S
ome of the less romantic workers gave their seams mere numbers—Newbury No. 2, or simply No. 7 or No. 11. Others were named for obvious reasons—the Great Course, the Little Course, the Standing Coal, the Main Coal, the Nine Inch, the Coking Coal. And then there were the seams with stranger names, no longer easily explicable: the Slyving, the Dungy Drift, the Globe, the Perrink, and the Kingswood Toad.
Go work the Slyving today
, might be the order of the morning.
Try your luck with the Perrink
, or
climb down into the Nine Inch, if it’s not too wet afoot
.

The men who first found those seams and named them—after their favorite pub, perhaps, or a girlfriend, or a hill immediately above the mine—are long dead now, and such histories as have been written of the coalfield give the Mearns Pit, one of the lesser collieries in commercial terms, short shrift indeed. But when the
last truckload of coking coal left the last mine in Radstock for the Portishead Power Station in 1973, it was from one of the deep seams of the field, nine thousand linear feet in absolute terms
*
below the red earth that lay serenely and unconformably above the contortions of the coal.

The stratigraphical order in which the different types of rock were arranged in the coalfield, as the local miners knew and as William Smith learned from them all too rapidly, had an utterly predictable regularity to it. Smith would see and come to know the strata intimately as he saw them one by one, again and again, as the great winding chain lowered him still further down through the measures.

First there would be the sandstones themselves, with strange patterns of bedding about them. Some patterns were large and reminiscent of dunes, other patterns were small, like the ripples to be found on the beds of river estuaries. After a few dozen feet, the sandstones would peter out and be gradually replaced by argillaceous beds of more thinly bedded rocks, with finer, darker grains—muddy and silty, solidified versions of what one might find on the bed of a shallow river. Next there would be a bed with fragments of shells, recognizable as the kind of bivalves,
Carbonicola
and
Anthracosia
among them, that are found in rivers and abhor the dissolved salts of the sea.

Then there would be mudstones—softer, dark, friable rocks, suggestive of—well—solidified mud. Next, an indicative precursor of what would come next, there would invariably be a thin band of lighter-colored, harder rock stuffed with shells of a salt-water brachiopod like
Lingula
—a creature still to be found more
or less unaltered today, which lives today as Carboniferous
Lingula
did 290 million years ago, happily and resolutely among the salt and the wavelets on the seashore.

And below that—the coal. The seam might be the Globe or the Perrink or the Kingswood Toad, and whether it was nine inches or nine feet thick, it would always be overlain by the same facies and underlain by the same seat earth. However, and most important for the ever-observant William Smith, each seam would be subtly different: It might be colored richly and deeply black, it might be oily, flammable, stiff with flies and footprints and the relics of eminently burnable fossil vegetation—
Mariopteris
,
Annularia
,
Lepidodendron
—and then, suddenly, cut off in a matter of fractions of an inch, the whole black band would be underlain by a light band of nonflammable seat earth, in which once all the ferns, trees, and horsetails placed their roots and from which they gained their sustenance.

The pattern, Smith saw, was always the same, in mine after mine after mine: from top to bottom, Sandstone, Siltstone, Mudstone, Nonmarine Band, Marine Band, Coal, Seat Earth, and then again Sandstone, Siltstone, Mudstone, on and on. On top of everything, placid and unconformable, the red marls, the flatly sloping beds of the startlingly red red earth.

And through all of this, in mine after mine, in quarry after quarry, what was perhaps the most crucial realization of all in this time of early, primitive discovery—the fact that recognizable seams of coal would always be in the same position compared to one another. The Dungy Drift—identifiable by its thickness, its color, and its fauna and flora—was always above the Perrink. The Rudge was always above the Temple Cloud. Never once—unless the Variscan folding has turned the whole bedding upside down, and a skilled observer could always tell if a rock bed was the right way up or not—would the Slyving be anywhere other than above the Great Course and the Firestone. It would always be well below the Withy Mills Seam and what the miners had christened the Pensford Forty Yard.

And that, in essence, is what William Smith first learned, both from the miners that he met and from the sections of the underworld that he saw. He understood for the first time that geology was a science requiring observations in three dimensions. He could make maps and make surveys of the visible upper dimensions of the landscape with ease—anyone with a modicum of a skill could do that. But to see
below
the surface, to observe or
extrapolate the imaginable third dimension underground—that was a new skill, possessed by very few, and yet that had a potential that Smith was soon going to recognize and exploit.

The Somerset Coalfield.

But first he had to grasp and set down on paper the importance of what he had just seen. He pondered on what he remembered; he pored over his notes. And he promptly wrote down in his diary what it was that he realized—that to judge from what he had seen at all these pits around his farm at Rugborne, he could make a firm pronouncement about the nature of sedimentary rocks—a pronouncement that he suspected had never been made before.

In his opinion, he wrote, all the rocks that had been laid down as sediments at a particular time in a particular place are laid down in a way that has much the same characteristics, and most particularly just the same fossils, and always appear in the same vertical order, in the same stratigraphical order, no matter where they are found.

He clarified his theory with examples. The coal measures in the south of the Somerset coalfield, near Radstock, for example, display a specific order. There is a Sandstone, a Siltstone, a Mudstone with
Carbonicola
, another Siltstone with
Lingula
, then the four feet of the Temple Cloud coal seam, back to Sandstone and Siltstones and then the Newbury No.2 seam and the Globe seam.

Using Smith’s new theory it would be possible, by noting the types of fossils he found, to forecast, and then to confirm, that ten miles to the north, at High Littleton, there would be exactly the same order. The Temple Cloud coal with its fossils would be lying above the Newbury No.2 with its slightly different ferns and fossil leaves, and the Globe with its peculiar collection of once-dead inhabitants would be down at the base. In between would be just the same Sandstones and Mudstones, just the same
Carbonicolae
and
Lingulae
as back at Radstock. Perhaps not the same thickness. But always, always in the same order. Never—if
the beds were lying right side up—would the Globe be at the top, never would the
Lingula
be found above the
Carbonicola
.