Abstract

Dr M. D. Max noted that the authors have shown the Gibbs Fracture zone as a NE–SW trending ‘feature’ in continental crust, linking faults in Newfoundland with proposed structural lineaments in Ireland. In fact, the Gibbs Fracture zone is a transform fault developed entirely within oceanic crust and cannot be referred to in the manner proposed by the authors. On a reconstructed closing of the north Atlantic, the Gibbs Fracture zone essentially disappears. It may link major structural lines in Newfoundland with those passing across the Irish continental shelf but only by a mechanism which would be comparable to wrench dislocation utilizing a transform site. The Gibbs Fracture zone may have been initiated as a point on a NE–SW suture which penetrated to the base of continental crust and in some way localized the initiation of the Gibbs transform, but a discussion of this possibility would be too lengthy to fully expand upon here.

The structural situation of Connemara and its Dalradian rocks does not fit into the authors' synthesis, which in all of their cross sections showed only oceanic crust to the south of the Ox Mountains horst. The implication of the authors' interpretation regarding the positioning of Connemara south of their important Southern Uplands Fault is that either all of Connemara is allochthonous or that Dalradian sedimentation was continuous on more than one crustal plate. Surely it would be simpler to do as the authors suggested indirectly from their last figure, and to pass the important

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