G. H. Kinahan — Archwan Rocks. 507 



said to be an " undoubted line of a double hiatus ! ! ! the rocks on 

 one side being Archfean, and on the other the equivalents of 

 the Ordovicians." Yet on both sides of such boundaries there are in 

 places identical rocks ; this difficulty has, however, been got over by 

 mapping all I'ocks inside the lines as gneiss, and those outside as 

 schist — regardless of their lithological characters. 



If the Fintown markings are not fossils, all the rocks belovs^ the 

 unconformability may be of any age, from Arenig to Archgean, hut all 

 must he included, as they are portions of one regular series. They, 

 however, cannot be the American Archaean, but, possibly, under such 

 circumstances (that is, the Fintown markings not being fossils), they 

 may represent the unnamed passage beds between the Archeeans and 

 the Primordial. 



In the Co. Tyrone, the rocks of the Slieve Gallion district are 

 more or less similar, lithologically, to the Huronians of Ontario. To 

 the south of them there is a well-marked break in time between 

 them and the fossiliferous " Pomeroy beds " (Llandovery ? ). North- 

 ward they are bounded by schistose rocks that lie on them uncon- 

 formably ; yet, but for this unconformability, the rocks above and 

 below it are lithologically so similar, that they might be con- 

 sidered as belonging to one group. These Slieve Gallion rocks, 

 although having lithological and other characters that might possibly 

 suggest an Archwan age, are evidently, as has been pointed out in 

 previous writings, the eastern extension of the rockg of the Pettigoe 

 District, South Donegal, in which case they belong either to the 

 Arenig or the Cambrian. The Pettigoe rocks in the new classification 

 have not been given a brevet rank, but are said to be the equivalents 

 of the Ordovicians. 



The most northern portion of Ireland, Innistra Hull, off Malin 

 Head, Innisowen, Co. Donegal, consists of gneiss. Possibly this 

 may be a bit of the Laurentian Hills, separated by a convulsion of 

 nature and strayed away, to be stranded and find a home off the 

 coast of Ireland. More probably, however, it is of Arenig age. 



It should be mentioned that the natural unconformity in the raeta- 

 morphic rocks of Ulster is treated very cavalierly ; as in some places 

 it is recognized and pointed out as " the undoubted proof of the 

 Archgean age of the rocks below it," while in all places whei'e its 

 position proved that the gneiss and schists below it must be portions 

 of one and the same series, it is ignored and is said not to exist. It 

 may also be interesting to record, that the two advocates for the 

 presence of Archeeans in Ireland are at variance ; as the one rejects 

 the idea of there being Archeeans in South-east Wexford, while the 

 other seems to say that there cannot be ArcliEeans in Donegal, as the 

 so-called " Laurentian gneiss" is an intrusive mass. 



