Drs R. A. Chadwick and A. Whittaker write: whilst welcoming Williams and Brooks’ analysis of the structural implications of our crustal cross-section beneath southern England, we feel that some of the criticisms of the seismic interpretation are unjustified and that their structural conclusions are incorrect. Below, we deal with their comments in sequence as they appear in their text.

First, we acknowledged in our paper (Chadwick et al. 1983, p. 899) that our interpretation of the deeper seismic events was necessarily speculative since much of the geological section is well beyond the limit of existing boreholes. However, it is important to recognize that our published section is the simplest interpretation which adequately reconciles the seismic reflection data with known Palaeozoic geology and the subsequent Mesozoic and Cenozoic evolution of the area. Williams and Brooks admit that our interpretation of southerly dipping events T1, T2 and T3 as thrusts is reasonable but state, correctly, that this is unsubstantiated. Many long, deep seismic profiles from various parts of the world show seismic reflection events that have been interpreted as thrusts, but our critics may not be aware that in northern France and Belgium, reflection events on seismic sections have been drilled and shown to be thrusts in the Variscan foldbelt south of the Brabant Massif (Bless et al. 1977; Bouckert & Paproth 1980).

Doubt is expressed by the authors about our interpretation interpretation of events R4 and R5 on part of line 79-01. Our interpretation that it represents an angular unconformity is

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