Worm burrows are another feature often found in sandstone that contains fossil traces. It is a kind of bioturbation, the preserved marks of plant or animal activity, including the burrowing of worms, insects, mussels, or clams, for example. Although Hitchcock named more than 50 species of invertebrate ichnofossils from the Hartford and Deerfield basins, these traces may never be confidently related to the exact organism that made them.