32 Scientifio Proceedings, Royal Dublin Society. 



much more plain than that between the Ordovician and Old- 

 hamians [Bray Head series) in south-east Ireland. 



The statement that some of the limestones in the Derryveagh 

 district (Grartan Lake) are conglomeritic is evidently incorrect. 

 The limestones, in which there are small pieces of quartzose and 

 micaceous materials, are on sheared rocks, in which the original 

 layers and partings, by shearing, have been broken up into frag- 

 ments, as can be proved in Scraigs and elsewhere ; while the supposed 

 inlying granite boulders are only the granitoid concretions that are 

 found everywhere in highly-metamorphosed limestones. 



Summary. 



The officers of the Geological Survey seem to have come to the 

 following conclusions, viz. : — 



All the pre -Carboniferous rocks in county Donegal belong to 

 one series, some portions being more sheared than others. 



The granitic gneiss and the foliated granite were all erupted at 

 one and the same time. 



Our conclusions are as follows : — 



These Donegal rocks belong to distinct geological periods. 



The Kilmacrenans (Grranitic and Schist series) are possibly pre- 

 Cambrian, and equivalents to one of the groups in the American 

 " Algonkian." 



The Kilmacrenans are undoubtedly capped unconformably by 

 the Killygarvan series. This is shown by the fact that in the basal 

 groups of the latter (the Grreat or Lough Salt quartzite) there are 

 fragments of the Kilmacrenans. There are also other proofs of 

 their unconformability, as above-mentioned. 



The Manorcunningham series may also lie unconformably on 

 the rocks of the Killygarvan series. This, however, has not been 

 positively proved. 



The Granitic gneiss and Foliated granite associated with the 

 Kilmacrenans are in part metamorphic and in part intrusive. 



Instead of one, there have been, at least, four or five periods of 

 granite intrusion. One or more intrusions occurred before the 



