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Excerpt of Earth by Richard Fortey
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Near the tip of the southern peninsula, Sorrento commands a wonderful prospect of Mount Vesuvius across the entire Bay of Naples. From this steep-sided town, Vesuvius looks almost the perfect, gentle-sided cone. It could be a domestic version of Mount Fuji, the revered volcanic mountain in Japan. It can appear blue, or grey, or occasionally stand revealed in its true brown colours. On clear days Vesuvius is starkly outlined against a bright sky: a dark, heavy, almost oppressive presence. Or on a misty morning its conical summit can rise above a mere sketch or impression of the lower slopes, which are obscured in vapour, as if it were cut off from the world to make a house for the gods alone. At night, ranks of lights along Neapolitan roads twinkle incessantly. Vesuvius is often no more than a dark shape against a paler, but still Prussian blue sky. The lights might persuade you that the mountain was still in the process of eruption, with points of white illumination tracking lava flows running down the hillsides. From Sorrento, you can make of Vesuvius what you will, for within a day it will have remade itself.

The Bay of Naples is where the science of geology started. The description of the eruption of Vesuvius and the destruction of Pompeii in a.d. 79 by Pliny the Younger is probably the first clear and objective description of a geological phenomenon. No dragons were invoked, no clashes between the Titans and the gods. Pliny provided observation, not speculation.

Not quite two millennia later, in 1830, Charles Lyell was to use an illustration of columns from the so-called Temple of Serapis at Pozzuoli, north of Naples, as the frontispiece to volume 1 of the most seminal work in geology—his Principles of Geology. This book influenced the young Charles Darwin more than any other source in his formulation of evolutionary theory: so you could say that the Bay of Naples had its part to play, too, in the most important biological revolution. Everybody who was anybody in the eighteenth and nineteenth centuries visited the bay, and marvelled at its natural and archaeological phenomena. For geology—a latecomer to the pantheon of sciences—the area is the nearest thing to holy ground that there is. If you were going to choose anywhere to retrace the growth in our understanding about how the earth is constructed, what better place to begin? Where else more appropriate to explain first principles? The long intellectual journey that eventually led to plate tectonics started in this bite out of the western shin of Italy's boot-shaped profile. A voyage around this particular bay is a pilgrimage to the foundations of comprehension about our planet.

Everything about Sorrento is rooted in the geology. The town itself is in a broad valley surrounded by limestone ranges, which flash white bluffs on the hillsides and reach the sea in nearly vertical cliffs—an incitement to dizziness for those brave enough to look straight down from the top. Seen from a distance, the roads that wind up the sides of the hills look like folded tagliatelle. Stacked blocks of the same limestone are used in the walls that underpin the terraces supporting the olive groves. In special places there are springs that spurt out fresh, cool water from underground caverns. These sources are often flanked by niches containing the statue of a saint, or of the Virgin: water is not taken for granted in these parts. There are deep ravines through the limestone hills, probably marking where caves have collapsed. The country backing the Bay of Naples is known as Campania, and the same name, Campanian, is applied to a subdivision of geological time belonging to the Cretaceous period. If you look carefully on some of the weathered surfaces of the limestones, you will see the remains of seashells that were alive in the age of the dinosaurs. I saw some obvious clams and sea urchins, belonging to extinct species, emerging from the cliffs as if they were on a bas-relief. A palaeontologist can identify the individual fossil species, and use them to calibrate the age of the rocks, since the succession of species is a measure of geological time. The implication is clear enough: in Cretaceous times all these hilly regions were beneath a shallow, warm sea. Limy muds accumulated there as sediments, and entombed the remains of the animals living on the sea floor. Time and burial hardened the muds into the tough limestones we see today. They are sedimentary rocks, subsequently uplifted to become land; earth movements then tilted them—but this is to anticipate. What one can say is that the character of the limestone hills is a product of an ancient sea.

Excerpted from Earth by Richard Fortey Copyright © 2005 by Richard Fortey. Excerpted by permission of Knopf, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.