Pcdceozoic Rocks of Galway and elsewhei-e in Ireland. 355 



hills to Oughterard, and thence westward to Clifden, we find the 

 same series of strata around three sides of the Great quartzite 

 (series B 6) of the Connemara hills ; while outside these rocks, 

 except to the south and south-east of Oughterard, where they 

 are changed into gneiss or granite, we find the rocks of the 

 Great micalite (B 10) and the Hornhlendite (B 11) series ; which 

 appears to me also strong evidence against the rocks south of the 

 Clifden and Oughterard valley being of Laurentian age. 



In conclusion, I would specially point out that I have never 

 asserted that there are no Laurentian rocks in Donegal ; but I 

 do assert that conclusive proofs of their existence therein have 

 still to he produced. Years ago Dr. Haughton classed the 

 granitic rocks of Donegal and Galway together, and now Dr. 

 Hull states he has no hesitation in referring both to the same 

 geological time, while Dr. Sterry Hunt has stated that certain 

 altered Palgeozoic rocks, later than Laurentian, cannot be dis- 

 tinguished from some of the Donegal rocks. If therefore these 

 Donegal rocks are lithologically similar to those of Galway and 

 to the Cambro-Siluriaus of America, one of the arguments in 

 favour of their being Laurentians falls to the ground. 



Of the area near Belmullett, N.W. Mayo, I have only a limited 

 knowledge, having been there only for a few days; but on 

 seeing the rocks I was at once struck with the great difference 

 between them and those with which they were associated, and, 

 as I have already mentioned in a previous communication to the 

 Society, with their similarity in many peculiarities to the granitic 

 rocks of Carnsore, county Wexford ; for which reason I suggested 

 that they were probably of Cambrian age.* In regard to the other 

 areas of supposed Laurentians, I believe that elsewhere I have 

 given better reasons for supposing them to be of Cambrian age"f- 

 than any which have since been put forward in support of their 

 being Laurentians ; it is therefore unnecessary to repeat them. 



I have observed that some, at least, of the Laurentianists, 

 when it suits them, lay great stress on the lithological characters 

 of rock at great distances from one another ; while, if these 

 characters do not support their theory, they get rid of the 

 difficulty by saying that the change is not greater than what 



* Scientific Proceedings of the Eoyal Dublin Society. Antea page 143. 

 t " Supposed Upper Cambrian rocks." Eoyal Irisli Academy Proceedings, 2nd Series, 

 Vol. iii. (Science), page 34;-i. 



