A spiral dislocation with axis perpendicular to the lattice planes of a layer lattice converts the disconnected sheets to a connected helicoid. Crystal properties dependent on propagation effects and so strongly anisotropic in the layered crystal may approach isotropicity as intra-plane parameters can now dominate inter-plane propagation. A single defect may thereby have a macroscopic effect on semiconduction and photoduction, magnetic susceptibility, specific heat, and other properties. Substances in which such effects may exist are listed.

• Received 15 February 1954

DOI:https://doi.org/10.1103/PhysRev.95.370