KiNAHAN — A New Beading of the Donegal Rocks. 31 



in common with them, while various aqueous deposits are more or 

 less similar. 



In a recent Paper by Dr. A. Greikie/ he says that the " Conne- 

 marians," or metamorphic rocks of Connemara (Gal way), are some 

 of the oldest rooks not only in Ireland, but also in the world. 

 The latter statement is undoubtedly incorrect, as they evidently 

 are metamorphosed fragmentary rocks ; while I suspect that as to 

 age, the Donegal gneissose and schistose series are the older. 



Before concluding, it is necessary to mention the writings of 

 Professor Jukes and others relative to this subject. Grriffith 

 pointed out, years ago, that there were discordances between the 

 older rocks of Malin Head, those of Slieve Gallion, and those of 

 the Glen Lough District, and the Later Rocks. Harkness said that 

 the Malin rocks were the equivalents of the " Upper pre-Cambrian 

 rocks of Scotland ; " Jukes suggested that the Older Eocks were 

 possibly Laurentians ; while Hull has classified the older Donegal 

 rocks as representing different groups in the Archseans. 



I may again state my belief that it would be very rash to 

 assert that any of the Irish rocks are the equivalents of the 

 American Laurentians; but from what the American geologists 

 have proved I now believe we may have in Donegal equivalents 

 of some of the " Gap-rocks," that is of the Algonkians or Ontarians 

 of those geologists. 



I am now convinced that Professor Hull was correct in saying 

 that the Great quartzite of the Lough Salt Hill and of Scraigs 

 (Finn Yalley) lies unconformably on the strata to the northward. 

 He, however, afterwards went astray, from allowing his assistants 

 to map the gneissose quartzite and the Great quartzite as one ; and 

 thereby missing all proofs of the unconformability. The old and 

 new quartzite rocks, however, as already mentioned, misled the 

 early American geologists ; and now, in the county Donegal, it 

 has been a stumbling-block to the officers of the Geological 

 Survey, from the Director- General downwards, except, perhaps, 

 to the Petrological Officer, who, from what he has written, seems 

 to recognize the difference between them. The evidence for an 

 unconformability in the rocks of the county Donegal is, however, 



1 " Eecent Eesearches into the Origin and Age of the Highlands of Scotland and. 

 the W^est of Ireland."— -Soy. Inst. Gt. Brit., June 7, 1889. 



