Hill, dale, and dry stone

Layers of limestone in this pastural portion of Northern England not only define the rolling landscape, they provide prime construction material for the walls corralling the area's wooliest denizens. Generations of skilled stonemasons have carefully arranged these stacks of limestone slabs that vary widely in size and shape, using techniques that maximize surface contact between the stones. Thanks to the everyday science of friction, a well-built dry stone wall can be as sturdy as solid concrete. The walls here in the Yorkshire Dales collectively stretch 5,000 miles, many of them several centuries old.