582 Proceedings of the Royal Irish Academy. 



bedding, while one or more boundaries may be fault lines, as if such, 

 masses had acted as groynes during the thrusting and other move- 

 ments of the associated rocks. Quartz-rock, however, occurs also in 

 places as dykes, while these massive sandstones never do so. The 

 Rev. Professor Blake, in his Paper on the "Monians " of Anglesey, 

 mentions the quartz-rocks, there called " quartz knobs," and seems to 

 be inclined to believe that they are eminently characteristic of Cam- 

 brian and Pre- Cambrian groups. This, however, is not the case in 

 Ireland, as in the Feakle district, county Clare, quartz-rocks occur at 

 the base of the Lower Carboniferous sandstone. In Slieve Partry, also 

 near Louisburgh, both in county Mayo, they occur at the base of the 

 Silurians. In the baronies of Kilmacrenan, Boylagh, &c., county 

 Donegal, they occur in the " Kilmacrenans," which are, probably, 

 equivalents of the " Caradoc sandstone." In South "Wexford, in the 

 Bannow and Taghmon district, they occur both in the Ordovicians and 

 the Oldhamians ; and near Greenore, in the same county, at the base of 

 the Ordovicians. In granite they occur at Oughterard, county 

 Galway (of which specimens are in Trinity College, Dublin), also 

 north of Tinahely, near Hackettstown, on the E. and JN". E. slopes of 

 Mount Leinster, and at Kiltealy, &c., counties Carlow, Wicklow, and 

 Wexford. This granite of Leinster is newer than the associated rocks, 

 which from their fossils are said to be Ordovicians. 



The quartz-rocks of Kiltealy and Mount Leinster occur as veins 

 associated with the granite veins, that nan rudely parallel to the 

 boundary of the mass of the granite, being in regular courses and 

 having a similar underlie to the granite veins. It is possible that they 

 should be more correctly classed as vein quartz. They have, however,, 

 characters similar to those of the intrudes at "WTiite Rock, north of 

 Tiuahely, and at Eagle Hill, near Hackettstown: being more or 

 less clastic, having false bedding lines, and Professor Sollas's "dirt 

 bands." The Eagle Hill intrude is eminently peculiar, as in part it 

 is quartz-rock that graduates into a conglomeritic silicious rock, the 

 latter graduating into a conglomeritic granitic rock. 



These rocks, associated with granite, have all the characters relied 

 on by Professor Sollas as proofs that quartz-rock is only a silicified 

 ordinary sandstone ; yet none of them could ever have been ordinary 

 sandstone ; while such characters would result from their having been 

 deposited by hotsprings, as has been suggested by the present writer 

 in previous publications.^ 



1 Geology of Ireland ; also "Quartzite and Quartz Eock," Transactions of the 

 Manchester Geological Society, vol. xiv., part xv., pp. 326, &c. 



