Abstract

Dr I. P. Tunbridge writes: In a recent paper, M. T. Holder & B. T. Leveridge (1986) proposed that the Rhenohercynian Variscides of Belgium, Germany and Cornwall were in tectonic continuity prior to late Carboniferous offset along the Bristol Channel–Bray Fault. They further proposed that a subduction zone extended along the line of the present English Channel and continued eastwards to the south of the Ardennes and Rheinisches Schiefergebirge. On two major points this interpretation is at variance with published evidence.

Firstly, Holder & Leveridge state that the Bristol Channel Landmass can be regarded as a westward extension of the Ardennes Massif of N France, and that this belt acted as a source for the Hangman Sandstone Group in N Devon. On the basis that this assumption is valid, they develop the proposal that the Gramscatho Group of S Cornwall represents part of a continuous flysch belt extending 800 km along strike. However, Tunbridge (1986) has clearly demonstrated that the Bristol Channel Landmass cannot be regarded as a continual ridge active throughout Devonian times and that it did not source the main part of the Hangman Sandstones. The sources in the Bristol Channel were localized and short lived, activated by strike-slip movements along the Bristol Channel Fault Zone. Furthermore, it is hard to see from Holder & Leveridges’ own reconstruction how the Ardennes Massif and sources associated with the Bristol Channel Fault Zone can be matched if the Bristol Channel Fault is continued into the Bray Fault of north

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