National Geographic : 2010 Jan
his Hebridean journey with complaints about the di culties of travel and the rustic accom- modations that he endured. But even as Johnson grumbled, a di erent set of ideas about the value of rugged places was gaining importance. Scottish Enlighten- ment thinkers, particularly philosopher David Hume and geologist James Hutton, unshackled intellect from piety, insisting that the ways of the world be learned by direct experience, rather than by reference to ancient and sacred authorities. To these men nature was not merely a wilderness to be tamed; it was the Earth's own textbook. Some of its most dramatic pages were read on the Hebrides. In 1800 geologist Robert Jameson (who later served as Charles Darwin's professor at the University of Edinburgh) pub- lished Mineralogy of the Scottish Isles in two volumes, o ering detailed descriptions of hun- dreds of Hebridean sites. On Islay, Jameson noted shell deposits far from the highest tides: "proofs," he wrote, "of the retiring of the sea from the land." Scientists now know that these fossil beaches, elevated as much as 115 feet above the present waterline, record the passing of the last great ice age. As glaciers blanket- ing the island began to melt 15,000 years ago, relieving it of the huge weight of ice, the land began to rebound, eventually li ing the coast- line high and dry from the sea. On Skye, Jameson declared that "this island appears, at some former period, to have been very much exposed to violent convulsions." e spiky arc of the Black Cuillin range, ris- ing more than 3,000 feet above sea level, is indeed the remains of a volcano. e outer structures have long since disappeared, reveal- ing the stark and convoluted shape of the deep magma chamber that seethed here 60 million years ago. Jameson stopped short of the westernmost isles, so he missed the chance to catalog the striped and mottled rock that forms the foun- dation of the Outer Hebrides. Named for the Isle of Lewis, where it was rst described, Lewisian gneiss was born from volcanic activity deep in the crust more than three billion years ago. Intensively and repeatedly altered, li ed up by complex tectonic shi s, and revealed by massive erosion, it is the oldest rock in the British Isles and among the oldest in Europe. Perhaps the most evocative place to encoun- ter Lewisian gneiss is in the great stone circle at Callanish, overlooking Loch Roag on Lewis. Erected between 4,500 and 4,900 years ago, the Callanish stones may have been standing lon- ger than the central ring at Stonehenge. Little is known for certain of the builders beyond their obvious engineering prowess, but it seems tting that one of the earliest monuments to the human occupation of the Hebrides should have been cra ed of this immensely old rock. Other standing stones dot the isles, along with Bronze Age burial cairns and stout Iron Age forti cations---most likewise built from Lewis- ian gneiss. e crumbling remains summon up the spirits of mighty warriors, the terror of villagers attacked from the sea, and the deter- mination of farmers, shepherds, and sherfolk to make their homes on the edge of the world. e romance of these brooding ruins speaks powerfully to Michael Robson. e old tales, he says, "however extravagant and impossible at times, o en have a measure of authentic- ity about them." Like the Enlightenment zeal Author Lynne Warren is a senior editor for the magazine. Photographer Jim Richardson is at work on a book about Scotland's whisky country. Nature was the Earth's own textbook, and some of its most dramatic pages could be read on the Hebrides.