The British Association: Section C—Geology


    On the Laurentian Beds of Donegal and of other Parts of Ireland, by Prof. Edward Hull, LL.D., F.R.S., &c., Director of the Geological Survey of Ireland.—After a perusal of the writings of previous authors, and a personal examination made in the spring of 1881, in company with two of his colleagues of the Geological Survey, Mr. R. G. Symes, F.G.S., and Mr. S. B. Wilkinson, the author had arrived at the following conclusions:—1. That the Gneissose series of Donegal, sometimes called “Donegal granite,” is unconformably overlaid by the metamorphosed quartzites, schists, and limestones which Prof. Harkness had shown to be the representatives of the Lower Silurian beds of Scotland (Quart. Journ. Geol. Soc., vol. xvii. p. 256). This unconformity is especially noticeable in the district of Lough Salt near Glen. 2. That the Gneissose series is similar in character and identical in position and age with the “Fundamental Gneiss” (Murchison) of parts of Sutherlandshire and Ross-shire, and is therefore, like the latter, presumably of Laurentian age. That the formation is a metamorphosed series of sedimentary beds, has been shown by Dr. Haughton and Mr. R. H. Scott. 3. That the north-western boundary of the Donegal gneiss is a large fault between the Laurentian gneiss and the metamorphosed Lower Silurian beds, owing to which the older rocks have been elevated, and by denudation have been exposed at the surface. 4. That the Cambrian formation of Scotland is not represented in Donegal, and that the unconformity abve referred to represents a double hiatus, and is of the same character as that which occurs in Sutherlandshire, in the district of Fornaven and Ben Arkle, where the Lower Silurian beds rest directly on the Laurentian gneiss. 5. That Laurentian rocks may be recognised in other parts of Ireland, as in the Slieve Gamph and Ox Mountains of Mayo and Sligo, at Belmullet, and in West Galway, north of Galway Bay, where the rocks consist of red gneiss, horneblende rock, and schist, &c., similar to those in Donegal; also possibly in Co. Tyrone, as suggested by Mr. Kinahan.

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    The British Association: Section C—Geology. Nature 24, 471–475 (1881).

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