Seashell Sundial

Down on the beach a boy in green swimmers was building a sundial. He had stuck a long driftwood branch into the wet sand and set seashells round it as the shadow moved, a different one each hour. As he pushed a crab claw into place I asked him, "How do you know what number each shell is?" He shrugged. "Doesn't matter," he said. "They'll all wash away before the sun comes back round."