The helical shape of certain burrows is interpreted in terms of 2 components of movement which determine the helical path of the burrowing organisms. One is a horizontal component of circular motion as a result of asymmetrical burrowing of a bilaterally symmetrical animal with paired appendages. The other component is inclination to the horizontal plane resulting from an oblique orientation to gravity. Helical burrows may be formed in a variety of environments by unrelated groups of organisms but individual types of burrows may have taxonomic or environmental significance in restricted parts of the geological column. A possible application in determining the direction of gravity at the time of the formation of these burrows would be more generally valid.