Limpets on the rocky shores of California are well known to travel across the rocks to graze on algae. They return to a particular home site before each low tide. So when the tide is down, you always see them "at home" digesting their meal. The California rocks are mostly rather soft; the grains of quartz and other minerals are only loosely cemented by calcium carbonate, and the limpets loosen the grains further by grazing with their radulae. The pits are shallow and oval, about the same size and shape as the underside of a limpet, and they may cover one whole side of a rock. See "Between Pacific Tides" or some other book on seashore life of California. Perhaps one of our Californian Conchlers can suggest a book at a more appropriate reading level? Andrew K. Rindsberg Geological Survey of Alabama