Kinahan — On Irish Arenaceous Rocks. 517 



equivalents of the rocks of the groups suggested by me in 1878, 

 in rny Geology of Ireland. 



In the Co. Gralway there are no rocks that can possibly be of 

 Liaurentian age, and the same thing may now be said of the Co. 

 Donegal. It is, therefore, only sensational geology to say that in 

 the intervening area (Mayo, Sligo, Leitrim, and Tyrone) there are 

 Laurentians, more especially as the metamorphic rocks therein 

 found are lithologically, and apparently stratigraphically, iden- 

 tical with the rocks in Gralway and Donegal. In the descriptions 

 of those counties in which Laurentians are stated to exist more 

 special details will hereafter be given. 



[As it has been assumed in some of the official memoirs that the existence of 

 Archaean rocks in Ireland has been proved, this subject has to be more promi- 

 nently mentioned than would otherwise be necessary. This recent finding of 

 Archaean has been very sensational from the first. Up to the end of 1880 Professor 

 Hull insisted that my classification "was probably wrong, as the oldest rocks in 

 Connaught and Ulster were proved by the work of the Survey to be of Lower 

 Silurian {Ordovician) age. But in January, 1881, when Drs. Hicks and Callaway 

 suggested that some of my Cambrians were Archaean, quite suddenly Professor Hull 

 •discovered Laurentians in Donegal and elsewhere in Ireland. After seven years of 

 steady work in the Counties Galway and Mayo, I classified the older rocks, and 

 subsequently traced them from Mayo into Sligo, Leitrim, Donegal, and Tyrone. The 

 rocks of the Twelve Pins (Bennabeola), Co. Galway, are lithologically more similar to 

 "the Huronians of Ontario, Canada, than the rocks in any other place in Ireland. 

 These are the rocks which, after Eozoon Canadense had been found in them, Murchison 

 -at one time suggested might be Laurentians ; but the rocks in the same county, said 

 by Professor Hull to be of Laurentian age, are evidently the youngest in this part of 

 Galway, and in the westward portion of his area, where some of the rocks are very 

 little altered, fossils possibly may at some time be found, for as yet they have not been 

 properly searched. The rocks of the Slieve Gallion district (Co. Tyrone) and those of 

 the Pettigoe district (Counties Fermanagh and Donegal) are partly like those of 

 Ontario, but in them are not found the calcareous rocks so well represented in Benna- 

 beola, Co. Galway. There are also other rocks in Donegal that are partly like the 

 Ontario rocks, such as those in the long tract embracing the Gartan Lakes [Loughs 

 Beagh and Akibbon), and extending from them north-easterly by Lough Keel to the 

 south end of Mulroy Bay — bits in which area are very similar to Ontario and Assina- 

 boia, as seen north of Lake Superior. The rocks of Crann Mountain, Co. Wexford, 

 are also somewhat like. As to the gneissose rocks, those of Galway, on the north 

 ■of Galway Bay (which evidently are metamorphosed Ordovicians), are lithologi- 

 cally more like the Laurentians of the Dominion and the States than any other rocks 

 in Ireland, if we except some small patches of very limited extent in Mayo, and 

 perhaps little bits in Sligo and Leitrim ; but the gneiss and schist of Donegal lithologi- 

 ■cally are very unlike, while apparently they are identical with the metamorphosed 

 Ordovicians of the Schuyllkill Riverjvalley, Pennsylvania [Mount Alban series, Hitch- 

 cock, or Hudson series, Dana). In 1884 and 1885 the late Gerrard A. Kinahan, as 

 previously mentioned (ante, p. 276), worked out an unconf ormability in central Donegal 



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