Current reconstructions of the late Paleozoic North Atlantic supercontinent show differences in detail, notably at more northerly latitudes. It is clear that the establishment of such geological “tie lines” demands detailed knowledge of the geologic structure of the outer shelves.

Data from marine geophysical surveys form speculative sub-Cenozoic geology for the continental margin west of the British Isles. The Great Glen fault is confirmed as a potential offshore structural tie line between the Caledonian and Appalachian orogens, although its relationship with the Cabot fault of Newfoundland remains equivocal. A convergent structural lineament crossing the Irish margin at about lat 53°N has no recognized counterpart in the surficial geology of the mainland, but with the Great Glen fault, it serves to delineate the offshore prolongation of the Irish Caledonides, some elements of which show close similarities to the Fleur de Lys Supergroup of Newfoundland. A more tenuous trans-Atlantic tie line involves correlation of an inferred east-trending fault on the Scottish margin at lat 56°N with the suggested prolongation of the Grenville front across Rockall Bank.

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