Plutarch, Moralia 13.1083d [De communibus notitiis adversus Stoicos ("On Common Notions Opposed to the Stoics")] reports this of Lynceus the Argonaut, whose x-ray vision and ability to see underground is praised in Apollonius of Rhodes (1.151-55). Pindar, Nemean 10.61ff., has Lynceus seeing robbers hiding behind an oak stump. So in Plutarch the "rocks" and "oak" seem to be meant literally. It's hard to see any relation in Plutarch's "rocks and oak" to Hesiod's proverbial "oak and rock" in Theogony 35. Any ideas?