Saturday, September 01, 2007

Stepping-stones


Here is a photo of the Blasket Islands in the west of Ireland, lying as usual in a steel-gray sea under a steel-gray sky, from a recent walk over Mount Eagle on the mainland. The headland where I'm standing is the westernmost point of Europe. Tomorrow I cross the sea to New England.

Four hundred million years ago, I might have walked there dry shod. At that time North America and Europe were part of a single landmass geologists call the Old Red Sandstone Continent. The part of that continent that is now the Dingle Peninsula was then an inland basin, and sands, muds, and pebbles eroded from the surrounding uplands were deposited on the floor of that basin. These eventually became the layered rocks that are the backbone of the Dingle Peninsula: sandstones, mudstones and conglomerates, gritty, well-consolidated and resistant. Meanwhile, to the south, the drifting continent of Africa was nudging northward, squeezing up against the underbelly of Europe and pushing the floor of an intervening sea back into the interior of the Earth. A great mountain range was lifted skyward, the ancestral Alps. Further north, behind the jagged peaks, the crust of the Earth was more gently crumpled in wavelike folds, like a carpet pushed from its edge. These folds reveal themselves today in the five rocky fingers of land and intervening bays that are the southwest coast of Ireland. Then, about 200 million years ago, the Atlantic Ocean started to open, as the Old Red Sandstone Continent fractured and was torn asunder by convection currents in the roiling mantle of the Earth. It opens still. When I return next summer, I will have an inch or so further to travel than I do tomorrow.