Trilobite: Eyewitness to Evolution Paperback - 2001

Summary

First line

Out of season, the bar of the Cobweb Inn at Boscastle is everything a pub should be.

From the jacket flap

With Trilobite, Richard Fortey, paleontologist and author of the acclaimed "Life, offers a marvelously written, smart and compelling, accessible and witty scientific narrative of the most ubiquitous of fossil creatures.
Trilobites were shelled animals that lived in the oceans over five hundred million years ago. As bewilderingly diverse then as the beetle is today, they survived in the arctic or the tropics, were spiky or smooth, were large as lobsters or small as fleas. And because they flourished for three hundred million years, they can be used to glimpse a less evolved world of ancient continents and vanished oceans. Erudite and entertaining, this book is a uniquely exuberant homage to a fabulously singular species.

Excerpt

Chapter 1

i

Discovery

Out of season, the bar of the Cobweb Inn at Boscastle is everything a pub should be. There is a low, heavily-beamed ceiling hung with antique bottles, and a plain floor which is a jigsaw of flagstones. Photographs of the local women's darts team hang on the wall, alongside framed, faded newspaper cuttings which record in print the several virtues of the inn. A log fire gives out rather more heat than is needed. There is no music save the low buzz of rich vernacular; in November, no Londoner ventures to the North Cornwall coast. The Cobweb is a slightly scruffy, comfortable old place, where you can talk if you need to, but if you feel like saying nothing you can just watch the flames in the hearth, and nobody will think you odd if a smile plays on your lips. It takes an effort of will to leave the dark, comfortable, nourishing womb of the inn, and emerge, blinking, into the bright world outside; but leave I must, because I have to find Beeny Cliff before the light fades. It can be dangerous out on the cliffs after nightfall.

Boscastle is tucked into a cleft on the wild northern coast of the long peninsula that completes south-west England, and it is built around a narrow harbour where the River Valency cuts down to the sea. It is an ancient place, where the cosmetics

of the tourist trade-Witchcraft Museum and knick-knack shops-have not quite succeeded in smothering a character that was born of slate and hardship. At one time the town comprised almost nothing but inns serving miners and seamen, of which the Cobweb is a survivor, and you can still imagine a dozen different signs advertising their wares all along the crooked street that leads to the haven. The houses are former inns, prettified with features that fail to disguise their boozy origins. The rough local stone gives the buildings their character. Even the Witchcraft Museum is a cottage with an ancient roof that sags crazily under the weight of Cornish slates. On this day the harbour is almost deserted, and I can imagine the place as it must have looked when the poet and novelist Thomas Hardy visited it as a young man, more than a century ago.

I leave the town on the northern side of the harbour where the path zig-zags up the side of the steep valley. There are gorse bushes which even at this time of year cheerfully wave sprigs of yellow pea flowers. Small birds secretively flit across the path-a wren and some stonechats-as if inviting me onwards. From up here I can see piers guarding the long, narrow harbour entrance, barriers that were already ancient when the first Elizabeth was on the throne. A cold breeze makes me wish I had put on an extra sweater, but I have luckily caught an interval between showers. Suddenly, I climb high enough to see the sea. This is one of those days when the furthest horizon is obscured in mist, as if the sea went on for ever. It is not stormy weather, but I can hear the growl of the surf smashing against cliffs, which weave in and out to the south, one after another, sheer to the sea. A white surf-line marks the junction:

With its long sea lashings

And cliff side clashings

as Hardy described this coast. The cliffs are dark, almost black, while the sea is strangely heavy, wrinkled like a pachyderm, so that only the lazily shifting white line of breakers serves to animate the prospect. The town in its secret valley has quite slipped from view; the solitude is absolute. I shelter from the breeze behind a wall, which is overgrown with rounded tussocks of sea campion and thrift. It is constructed mostly from blocks of slate; curiously, the slate slabs are placed vertically, so that they look like books set on their edges, pages towards you. I am accustomed to different,

horizontally-built stone walls around Oxford. The pattern is broken by occasional piers incorporating angular blocks of white, coarse-looking vein quartz. The artisans who built these walls knew their rocks. Slates stacked vertical will let the rainwater (and there is plenty in Cornwall) drain rapidly away, parallel to the way the rock naturally splits. Rubbly quartz is indifferent to all weathers and makes for obstinate pillars. Both rock types are now decorated with a leafy, frilly form of green lichen, which softens every stony outline in such a damp climate.

Now that I study the cliffs I can see that they, too, are made of the same black slates. This is why they seem so forbidding, so stern and dark. In places they are beetling (a word which only seems to apply to brows and cliffs) with teetering overhangs, fissured, and with obviously dangerous crags. These cliffs are a hymn to vertigo: "haggard cliffs, of every ugly altitude . . ." I pay careful attention to the narrow and slippery path; there has been a lot of rain recently, and one foolish step might have serious consequences. Tumbledown stone walls indicate that fields formerly extended very close to the top of the sheer edge, but now there is only a steep grassy slope between the walker and the airy heights where razorbills and fulmars wheel on the wind. The few, stunted trees on the slopes lean away from the fall as if their branches stretched in horror from the tumbling edge.

By the time I reach the top of Pentargon Bay I have some feeling for the geology. The dark rocks displayed on the inaccessible cliffs have surely suffered in a great vice of Earth movements, for they are tilted and crimped. No strata follow a straight line, instead they take off on a convoluted journey of their own. On the far side of the bay I can see a fissure that extends vertically from cliff edge to sea, which has been excavated by the elements over millennia. This is certainly a fault-a great fracture through the black rocks-a dislocation which must have once made the Earth shudder and tremble. Faults are the visible signatures of earthquakes, sealed for eternity in the rocks. The whole coast must have been gripped by a mighty upheaval causing the strata to crack and buckle. The evidence of a prehistoric paroxysm of the crust is imprinted on these heights.

Look harder, and evidence of tectonism is everywhere. Not far from the fault a stream follows a narrow valley which has been excavated along another plane of weakness in the rocks. Where the stream reaches the sea its valley is cut off abruptly at the cliff, and the brook suddenly plunges into a waterfall two hundred feet above the sea, where it is whipped up by the breeze into spray. Near the water-line there are caves and smaller crevices which have been excavated by the probing sea. Even on such a calm day I can hear the suck and cough of waves assaulting the slates, picking out the weakest spots where folds have cracked the strata, marking each small fault with a chasm or a hole. From time to time a wave rushes into a cave compressing the air within it-which then recoils with a report. It makes a sound like distant cannon fire, an irregular salvo fired in an orogenic war. Imagine the battery on a stormy day. Now it is possible to comprehend how thousands of years of erosion have eventually isolated stacks and islands, like Meachard off Boscastle harbour. In time, these outposts of land will be worn quite away and returned to the sea. I can identify white quartz in the matrix of the gloomy cliffs, as clearly as scribblings of chalk on a blackboard. There is even a patch where the quartz trace shows the strata to have been folded over completely-turned upside down. I can only speculate on the massive forces which have treated solid rock with such disdain. Thicker masses of quartz are aligned along the faults. Squeezed from the rock like serum from a wound, it congeals in the cracks. This must have been the source of those large lumps in the stone walls. Elsewhere, it fills in voids in stressed rock like some kind of mad spaghetti. Ultimately, though, quartz is tougher than slate, and survives as pebbles long after the country rock has been eroded away. I would be willing to wager that some of the rounded pebbles on inaccessible Pentargon beach far below me are made of quartz. They will outlast these cliffs, and-who knows?-maybe they will outlast the human species.

The sooty shales and slates were once soft muds-sediments-which accumulated deep beneath the sea. Time has transformed them: hardened them, elevated them hundreds of feet above present sea level, and folded them. But how much time?

Where I am standing now, close to the edge, there is a notice in red letters: Caution! Cliffs are liable to cracking. Take extra care. And it's true. A stack of shale is teetering outwards into the void. It is hard to escape a shiver of apprehension as you imagine the block tumbling over and over to smash to pieces far below. The next haven up the coast is called Crackington, the name encapsulating the precariousness induced by erosion.

I have a geological memoir for the Boscastle area tucked into my jacket pocket. From the geological map which sketches out the pattern of the outcrops of the rocks I can see something of the tectonic agony which is so patent in the cliffs: rock formations twist and turn over the mapped ground, which is criss-crossed by faults. I can identify exactly where I am standing, on the outcrop of the Boscastle Formation; in the dry language of science the slates are described as early Carboniferous (what in the US would be called Mississippian). This corner of the world has an extremely ancient origin, older than mammals, older even than dinosaurs. These black slates would already have carried their contorted signature as a guarantee of antiquity when Tyrannosaurus was king of the hill. When they were first laid down there were only tree ferns and cockroaches and cumbrous amphibians on land. Can there be a better place to reflect upon the vastness of geological time?

The erosion which I can both see and hear is ineffably slow. I could stand here all my life and notice little difference to the cliffs. Maybe a chasm excavated along a fault might seem subtly darker as its girth increased after an exceptional storm. Perhaps a rock fall would leave a scar cleared of campion and grass. But I am certain that when Thomas Hardy stood on this spot he would have gazed upon a comparable scene; my eyes now see what his once saw. To be sure, the vegetation would have changed, but the geological signature of the cliffs would have been legible in much the same way. How can we conceive of the time needed to wear away these cliffs to nothing, to convert all the massed slates into fine silt, quartz veins into pebbles-at first angular, then worn by the constant shuffling of the sea rounder and rounder, until they acquire the contours and colours of a hen's egg? Millennia are irrelevant, species come and go, and still the cliffs stand obstinate against the inroads of time. Yet given enough time even this rampart that seems to stand so unflinchingly against the surf will be reduced to nothing, and the flagstones on the floor of the Cobweb Inn will return to sediment, joining all the other works of Man, committed once again to the great cycle of change. Rocks are eroded to sediment: sediment is hardened to rock; rock is elevated above sea level by movements of the Earth, transformed by tectonics; and, thus raised, is once more subject to the assault of the elements. This is the great wheel of the Earth. If Gustav Mahler had taken the geological view, Das Lied von der Erde (The Song of the Earth) would have been

a cycle of erosion and reconstruction endlessly reiterated, enough to try the patience even of those who admire the most mantric of symphonies.

Cornwall once formed part of a vast mountain chain. It marked one end of the Hercynides, which snaked through Europe just as the Alps do today in the south. The patent folding of the rocks was the result of the slates being trapped in a great tectonic vice that showed no mercy. Rocks buckled, in an attempt to accommodate forces that were irresistible. Every tiny ruckle in the wall of Pentargon Bay is the legacy of suffering under a rule of tectonics so mighty that no mere rock could stand against the imperative of crustal stress. When the rocks were folded, structure was piled upon structure until mountains resulted. Clever geologists from the University of Exeter, like E. B. Selwood, have spent years trying to unpick the buckling. They have interpreted this stretch of coast not as merely folded, but as divided into great slices of crust which have slid over and past one another. Squeezed rocks could not absorb the forces by contortion alone, and were compelled to fracture. To attain equilibrium, vast broken slabs of rock larger than a parish slid away from the centre of the forces at a low angle, like the twisted thorn branches leaning away from the reach of the sea wind. Under the sole of these sliding masses weaker rocks were folded over and over, crumpled like a pack of playing cards in the hands of a ruined gambler. Every crack that was opened up, as the country was ground beneath the tectonic wheel, would be filled with vein quartz. Now, the eroded remains of these mountains lay before me. The lichen-covered stone walls were fabricated from the relics of ancient Alps. The farmer who orientated the slaty slabs with such care was conniving with tectonic forces of which he probably knew nothing.

Not many miles to the south, near Bodmin, a granite tor rises above the general plain. It is reminiscent of some stepped Mayan pyramid, not least in scale, but is entirely natural. The strange pile of enormous blocks is what remains behind when granite is weathered over many thousands of years. Even granite eventually succumbs to the onslaught of the elements, rain and wind and frost. But granite endures longer than shale, as I was to see in St. Juliot's churchyard, not far away. Granite, too, is part of the narrative of the vanished mountain chain, although its source was utterly different from the shales of the Cornish cliffs. It was crystallized from a liquid magma, hot and invasive, within the deep heart of the former chain. Look now: you can see big crystals of felspar, and maybe the sparkle of mica. These crystals tell the story of how a mountain chain drives crumpled rocks so deep into the Earth's crust that they melt, and brew a buoyant, hot broth of liquid minerals, which once more rises through the crust to crystallize and solidify as granite batholiths and plutons. Granite lies at depth beneath the Cornish peninsula, reaching to the surface under the boggy stretches of Dartmoor and Bodmin.

Media reviews

?[W]onderful reading about a charming group of gone-but-not-forgotten creatures.??Natural History

?[F]ortey gives a passionate and often lyrical account of his life with trilobites.??Nature

?Fortey is...a gifted writer who shares his knowledge with grace and verve.... Trilobite is about seeing and the search for truth.??The New York Times Book Review

Citations

• New York Times, 12/02/2001, Page 89
• Science, 06/05/2009, Page 1267