Mr W. B. Harland contributed the following definition to a discussion on terminology. For faults in which the primary motion is horizontal parallel to the fault trace (1) the general term is strike-slip faulting whatever the magnitude of the fault or movement. (2) Only if the fault zone appears to be a fundamental one, i.e. to have sufficient depth and strike-slip component to rupture the whole lithosphere should it be described as a transcurrent fault. (3) If the ends of any transcurrent fault are known or alleged to terminate in diverging lithosphere with spreading zones or converging lithosphere with subduction etc, the term transform fault should be used. This can be on a small scale as in an oblique transtension ocean spreading zone or on a large scale where the fault may equally pass through continental crust. Mr Harland might have added for further clarification that the above terms are all purely kinematic. Wrench faulting is a dynamic concept (i.e. in which the intermediate principal stress is vertical) and may or may not apply to any part of the above strike-slip fault. From this paper and that of Johnson et al. (Journal, in press) it is clear that the transcurrent (including transform) fault zones may involve some oblique horizontal motion exhibit by both strike-slip and dip-slip faults. The dip-slip faults will probably be reversed in transpressive zones and normal in transten-sile zones from time to time and place to place along the fault.

In reply the AUTHORS welcome Mr Harland's

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