CHAP. XXX 
VOLCANIC BRECCIAS OF COUNTY CORK 
5i 
what like a nodular felsite. This variety ends off rather abruptly to the 
north, hut swells out southward, and then runs out into a high, narrow head- 
land, in which it contains asbestos, as well as rounded crystals of hornblende. 
It has here disrupted the shales and sandstones, and near the junction is 
largely composed of fragments of them, the strata themselves being jumbled, 
bent, and broken up. 
The only semblance of a neck-like, mass of this volcanic fragmental 
material occurs on White Bull Head, where one of the bands expands about 
the centre of the ridge, and is there full ot large blocks of giej sand 
stone. The breccia appears to have filled fissures which have been opened 
between the bedding planes of the highly tilted strata, giving rise to long 
narrow dyke-like intercalations. We have seen that among the Carbon- 
iferous volcanic phenomena such dyke-like masses of agglomerate occasion- 
ally present themselves in the vents both of the plateaux and the puys. 
In one or two places I noticed what may be traces of clear age in the 
breccia. The rock is not one that would yield easily to the rearrangements 
required for the production of this structure, and the doubtful cleavage may 
be deceptive. If we are justified in regarding the introduction of this 
volcanic material as having necessarily taken place after the tilting ot 
the strata, we may not unreasonably infer further that the eruptions could 
only have been effected at no great distance from the surface. But the 
Carboniferous Slate in which these agglomerates lie is the lowest member 
of the Carboniferous system. As there is no known unconformability 
throughout this system in the south of Ireland, the whole of the rest of t le 
pile of Carboniferous strata, amounting to a depth of several thousand feet 
once probably extended over this region. It must, therefore, have been not 
only after the plication, but after extensive denudation of the formations that 
the fissures were filled with agglomerate. These geological changes no doubt 
occupied a vast period of time. While, therefore, no positive evidence lias 
yet been gathered to fix the age of these volcanic eruptions of the south- 
west of Ireland, it is tolerably clear that they cannot be assigned to the 
Carboniferous period, but must belong to some later volcanic epoch. They 
may be of Permian age, perhaps even as late as the Tertiary volcanic series. 
