This broad and engaging tour of the geology of the Appalachians explores how these mountains were formed, how they aged, and how we know. McPhee is a master of craft, interweaving disparate strands with intelligence and character. His goal here, I think, is chiefly to show how scientists work and live. He does not, I think, get it exactly right, but he gets more right than almost anyone else -- especially the scientist's respect for the data.