Wikipedia
Skolithos (formerly spelt Scolithus or Skolithus) is a common trace fossil ichnogenus whose original form consisted of approximately vertical cylinders. One well-known occurrence of Cambrian trace fossils is the famous 'Pipe Rock' of northwest Scotland. The 'pipes' that give the rock its name are closely packed straight tubes, which in this case were presumably made by a worm-like organism. The name given to this type of tube or burrow is Skolithos, which may be 35 cm (14") in length and between 2 to 5 cm (0.8 to 1.6") in diameter. Such traces are known worldwide from sands and sandstones deposited in shallow water environments, from the Cambrian Period onwards. Skolithos burrows have rarely been described from carbonates. Some burrows have a helical form. Skolithos is typically marine, but is also known from freshwater lacustrine settings. It is usually associated with high-energy environments close to the shoreline. Trypanites is a similar form but is excavated in hard substrates as a trace fossil. Also related are Ophiomorpha and Diplocraterion.