Urban geology

By Helen Gordon

Every weekend, as the buses rumble down Regent Street, people pile into the Apple Store to spend their savings on the thrill of the new. If they were to look down on their way in, they would feel the shock of the old. The pavement is made of grey sandstone, engraved with fine bands of curving lines—the ripples from the current of a river that flowed through what is now the Pennines, then a region of swamps, dense vegetation, high mountains and wide-open flood plains. The ripples are from 300m years ago.

This was during a geological period known as the Carboniferous. Mammals and dinosaurs had yet to evolve. On the land, amphibians moved among tree ferns and horsetails. The unnamed river contained tiny rock particles. As it flowed, these were deposited on the river bed and over time, through processes of compaction and cementation, they formed the sandstone known as Yorkstone—London’s traditional paving material. When you stop and stare down at the sandstone, you have a glimpse of a world that existed long before humanity.