Abstract
IN 1863 Dr.T. Sterry Hunt pointed out the resemblance of some specimens of rocks and minerals from Donegal which he had examined to those of the Laurentian series of North America. These rocks and minerals have been described by Dr. Haughton and Mr. R. H. Scott, who have pointed out that the “typical Donegal granite” is really a metamorphic bedded rock, containing in some places bands of crystalline limestone or marble. Outside the granite district are the newer series of schists, quartzites, and limestones, which occupy the whole of the Promontory of Innishowen, and were identified by the late Prof. Harkness with the Lower Silurian metamorphic series of the Highlands of Scotland. These two groups are shown on Griffith's Geological Map of Ireland, and it will be seen on an inspection of this map that the quartzite series is represented as terminating obliquely against the margin of the granite or gneiss. This obliquity has never (as far as I can discover) been explained. The prevalent opinion seems to have been that the newer series has been converted into the older by increased metamorphic action. For some time past I never studied Griffith's map without the impression that the obliquity was due to unconformity of stratification, and on the determination of this point plainly rested the question whether the granitoid gneiss was, or was not, of Laurentian (or “Archæan”) age.
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HULL, E. Laurentian Gneiss of Ireland . Nature 24, 81–82 (1881). https://doi.org/10.1038/024081a0
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DOI: https://doi.org/10.1038/024081a0