Books: How seaside rock shaped the world

Where should we start? In remotest Argentina, where a lump of shiny stone lay in the middle of the Field of Heaven? Or with St Hilda, who wasn't quite what she seemed? Perhaps with Henry VIII, who probably married Anne of Cleves for her alum works? Or down in the Southern Ocean with Captain Cook? Or maybe with William Buckland in a hyena's lair, full of the bones of bear, weasel, wolf, elephant, mastodon...

No, let's begin with the title. It is possible to tell that you have reached the end of the alum-making process, when the solution has reached precisely the right specific gravity, because a hen's egg will float on the surface. The Floating Egg is the alum-maker's secret. This arcanum is scarcely in the same league as the philosopher's stone: alum, while useful as a dye-fixative, is considerably less valuable than gold. Yet for centuries it brought wealth and industry to the North Yorkshire coast, near Whitby, after the discovery was made that the local cliff-shales contained the requisite raw materials to make several alum fortunes. Previously, the nearest place you could find such geology was in Flanders, not far from Cleves.

In the course of mining these cliffs during the eighteenth century, several enormous prehistoric fossils were found. Little ammonites, such as appear on the coat of arms of Whitby Abbey were already familiar. They were known as snakestones on account of the legend that the Abbess, the great St Hilda, had turned all the local snakes into stone. Now, however, vast 20 feet long icthyosaurs and plesiosaurs began to emerge from the rock, happily just when science was advanced enough to appreciate and preserve them. One can be seen in Houston, Texas, though unfortunately its head is missing. There is a more complete model in Whitby museum.

And so it goes on. The stories come tumbling out, each more unlikely and fascinating than the last, and all of them closely connected with this one little strip of coast. If you have never read a book about geology before, and didn't even think you were interested, Roger Osborne could change your life. He permits not a moment of tedium and his style is as varied as the composition of the earth. Sometimes it is briefly, sternly academic, providing formulae and definitions - of fluvial aggradation, catena, ganister and splay sandstone. Sometimes it is a racey narrative, as in the account of the discovery and identification of a cave (in Yorkshire, of course) in which ice-age hyenas had crunched up the bones of a bewildering variety of other animals. Dr Buckland, the scientist who analysed these remains, took a group of interested people to a travelling circus to watch a hyena at supper and prove his theory.

Osborne enjoys legend, including the story that the devil built Filey Brigg - or maybe it was constructed by witches, flying in egg-shells - and he can be dreamily romantic: after a storm "... the sea lay like an innocent reveller, sighing in its drunken sleep, while all around was strewn the devastation of its night of mischief ...". He quotes Claudius, Homer and Ptolemy as readily as he uses the findings of nineteenth-century geologists, or the diaries of his hero Captain Cook, who grew up in Staithes and whose vessel, Endeavour, was a flat-bottomed boat designed to carry coal along inshore waterways.

One particularly marvellous section concerns meteorites. Spanish conquistadores in South America discovered a lump of metallic stone in the wide plain they called Campo del Cielo, near Santiago del Estero: local legend said that it had fallen from the sky. Hoping it contained silver, they sent out exploratory parties to bring back samples for analysis: 17 chisels were worn out in the process of removing lumps, though alas no silver was found.

Osborne is intensely excited by geology and succeeds magnificently in communicating his enthusiasm. Yet, despite its light touch, despite dinosaur skeletons wandering across the pages, despite frivolous asides and flights of fancy, this is a serious book, provided with thorough notes and appendices bulging with further recondite information. Endearingly, Osborne loves aphorisms and sprinkles them liberally through his text, often to justify his catholic approach. Science, he says, "may not always be concerned with the dissolution of myth: it can live alongside some other kinds of understanding". Or, as Giorgio de Santillana put it: "Wisdom does not lie in turning away from appearances, but in mastering them".