AIOriVEESAKY ADDKESS OF THE PRESIDENT. 97 



ably see the remains of another group of vents which were active 

 over the east of Berwickshire. 



The Lower Old Red Sandstone tract of the North of Ireland was 

 probably deposited in the same continuous area with that of the 

 Midland Valley of Scotland. We find the sandstones, conglomerates, 

 and volcanic rocks well developed south of Campbeltown in Caatire, 

 and similar rocks appear on the Antrim coast at Cushendall, and 

 still more extensively in the interior between Pomeroy and Omagh. 

 Sheets of diabase and porphyrite, and occasional showers of tuff, 

 have been poured out in Tyrone among the sandstones and con- 

 glomerates, which in some places are largely made up of detritus 

 of the volcanic rocks. The sections visible in that district present 

 the closest resemblance to what may be seen in almost any part of 

 the Old Eed Sandstone tracts of Central Scotland. In one respect, 

 perhaps, the Pomeroy porphyrites possess a local peculiarity ; no- 

 where among rocks of this age have I noticed a more perfect flow- 

 structure. So marked is this structure in some cases (Sentry Box 

 Hill) that the rock splits into parallel flags, the amygdaloidal cavities 

 being flattened and drawn out in the direction of movement.^ 



In the South of Ireland the top of the Upper Silurian group of 

 strata is followed upwards conformably by the great series of red 

 sandstones and conglomerates known as the ' Dingle Beds.' 

 LithologicaUy these rocks present the closest resemblance to the 

 Lower Old Red Sandstone of Central Scotland. They occupy a 

 similar stratigraphical position, and though they have not yielded 

 any palaeontological data for comparison, there can, I think, be no 

 hesitation in classing them with the Scottish Lower Old Eed Sand- 

 stone, and regarding them as having been deposited under similar 

 geographical conditions. They offer one feature of special interest 

 for my present purpose, since they include a well-marked group of 

 contemporaneous volcanic rocks, which are quite unique among the 

 later Palaeozoic formations of this country, inasmuch as they include 

 acid rocks of the type of nodular felsites, like those so characteristic 

 of the Silurian period. 



The area where this remote and isolated volcanic group is best 



^ Farther south-west, near Boyle, in the county of Roscommon, certain 

 curious felspathic breccias in the Old Red Sandstone contain pieces of andesitic 

 and felsitic rocks, with fragments of devitrified glass, suggestive of the occurrence 

 of volcanic eruptions during their deposition, though no undoubted tuffs and 

 lavas appear to crop out in the narrow strip of the formation there exposed. 

 See, however. Jukes and Foot, Journ. Roy. Geol. Soc. Ireland, vol.i. (1866) p. 249. 



