16 Scientific Proceedings, Royal Dublin Society. 



in places come up against the Later Period Rocks, but never 

 extend into them. 



The Older Period Rocks were faulted and displaced prior to the 

 accumulation of the Later Period Rocks, and consequently none of 

 these ancient faults, although in places very numerous, extend up 

 into the newer formation. 



The Later Period Rocks, in a few places, can be distinctly seen 

 to lie unconformably on the upturned edges of the Older Period 

 Rocks. 



In the Later Period Rocks there are in places Boulder and other 

 fragmentary beds, the boulders and other fragments being derived 

 from the denuded portions of the Older Period Rocks. 



It is highly confirmatory of my work to find that the facts to 

 which I have all along appealed, as proving the unconf ormability 

 in the altered older rocks of Donegal, should be exactly similar to 

 those given by some American geologists in recent publications, 

 as indicating the unconformabilities in Wisconsin and elsewhere 

 in the Lake Superior region. It is also remarkable that the failure 

 of the older American geologists to distinguish one arenaceous 

 group from another should now recur among geologists of this 

 country. This should not have been so, as I had pointed out to 

 them the proofs of the difference in age of the distinct groups of 

 quartzites ; yet some of them have even gone so for as to say my 

 proofs were " physical impossibilities."^ 



^ Professor Hull, after his visit to Donegal with Messrs. Symes and Wilkinson, 

 stated he had proved an unconf ormability between the Later and Older Period Eochs ; 

 but afterwards it would appear as if he was unable to trace it out, as he allowed him- 

 self to be persuaded to say the self-evident proofs pointed out to him by me were not 

 satisfactory. "When only a short time stationed in the county, it appeared to me that there 

 must be an unconformability between the Later and Older Period Eocks, while there 

 also seems to be a second and later unconformability ; the latter, however, I never had 

 an opportunity of working out. The late Gerrard A. Kinahan, as already mentioned, 

 made a survey of part of Kilmacrenan ; and during it he came to the conclusion that 

 there must be rocks belonging to at least two distinct ages. At the time of his first 

 visit he had not seen the Canadian rocks ; but before his more detailed survey he had 

 done so. Before commencing this survey he was inclined to think that Professor Hull 

 was correct in stating that Laurentian rocks were to be found in Donegal ; but, after 

 his final examination, he came to the conclusion that, although there was an uncon- 

 formability, the line of this unconformability, as laid down by Professor Hull, was 

 incorrect, and that the older rocks could scarcely be the equivalents of the American 

 Laurentians, but that in many characters they were similar to the "Western Ontario 



