ANNIVKUSAKY ADDKlvSS OF Till) PUKSIDKNT. I 59 



conditions preclsoly like tlioso that determined the accumulation of 

 the Old Red Sandstone in the same region at a later geologic;! 1 

 period. And in that case, it is hardly possible to conceive that 

 these conditions could have been confined to the extreme south of 

 Ireland. We should certainly expect to moot with evidence of them 

 elsewhere, at least in the same Silurian region. 



While I hesitate to express a decided opinion in opposition to 

 the conclusions of such experienced observers as Jukes and ])u 

 Noyer, I incline to believe that the rocks in question really belong 

 to the Old lied Sandstone. If such shall finally be determined to 

 be their geological position, they will supply evidence that some at 

 least of the volcanic vents of the coast-line cannot be older than 

 the Old lied Sandstone. They are pierced by masses of soda-felsitc 

 and. by a coarse red agglomerate containing abundant pieces of 

 felsite. These volcanic rocks belong to the same type as those 

 which break through the undoubted Silurian rocks on either side. 

 They may thus come to prove a recrudescence of volcanic energy 

 in this same district at a much later geological period ; and a new 

 problem will arise to task the skill of the most accomplished field- 

 geologist and petrographer — to unravel the structure and history of 

 this chain of volcanic vents, and, in so doing, to detect and separate 

 the eruptions of Lower-Silurian time from those of the Lower Old 

 Ked Sandstone. 



Upper- SiLFRiAX Yolcaxoes. — The latest volcanic eruptions of 

 Silurian time yet definitely known took place during the accumula- 

 tion of the Llandovery, Wenlock, and Ludlow rocks in the far west 

 of Ireland. No satisfactory record of any contemporaneous pheno- 

 mena of a like kind has yet been met with in any other Upper- 

 Silurian district in the British Isles. There were at least two distinct 

 and widely separated centres of activity. One of these Isij in what 

 is now the wild mountainous tract between Lough Mask and the sea, 

 along the borders of Counties Mayo and Galway. The other is to 

 be sought among the headlands of Kerry, where the land projects 

 farthest west into the stormy Atlantic. The occurrence of the vol- 

 canic rocks in these remote areas and their geological horizon have 

 been clearly indicated on the maps of the Geological Survey. Thirty 

 years, however, have elapsed since some of the mapping was done, 

 and we must therefore be prepared to find it, more especially in its 

 petrography, capable of modification and improvement now. 



The more northerly of the two districts cml)races a tract of sin- 

 gularly rugged ground, composed in great part of conglomerates 



VOL. XLVII. ni> 



