Adirondack boulders were dropped by retreating glaciers and are among earth’s oldest rocks

Evidence

Glacial erratics stud the Adirondack landscape, granite boulders dropped in place when the glaciers got tired of rolling them and melted their way back home to the north. The granite in these parts is anorthosite, among the oldest rocks on earth and resistant to weathering. Most of the boulders have been rounded by their journey, but some still stand tall and sharp-edged, like this one, which is as big as a dump truck. — Robin Wall Kimmerer, Braiding Sweetgrass, 981

Categorization

• CANDY: Glaciers ‘getting tired of rolling boulders’ — vivid way to picture erratic deposition.