. Manual of the geology of Ireland. time. In the description of the Cambro-Silurianrocks of SE. Ireland it was mentioned that in the upper,ones, or those of the Ballymoncy scries, are sheets of beddedEruptive rocks. In the lower, or the Dark Shale series, the 184 Geology of Ireland. granitic roots of these sheets occur. Some of these rootsare silicious elvans ; others are granitone, or some othervariety of basic elvan ; and invariably surrounding, and inthe vicinity of, the protrusions of the basic elvans, theCambro-Silurian rocks have been altered by paropteticaction. As the rocks in which th
. Manual of the geology of Ireland. time. In the description of the Cambro-Silurianrocks of SE. Ireland it was mentioned that in the upper,ones, or those of the Ballymoncy scries, are sheets of beddedEruptive rocks. In the lower, or the Dark Shale series, the 184 Geology of Ireland. granitic roots of these sheets occur. Some of these rootsare silicious elvans ; others are granitone, or some othervariety of basic elvan ; and invariably surrounding, and inthe vicinity of, the protrusions of the basic elvans, theCambro-Silurian rocks have been altered by paropteticaction. As the rocks in which these protrusions are situatedare principally argillaceous shales, the altered rocks ingeneral are hornstones, but some green tuffose rocks havebeen changed into rocks like whinstone, and some siliciousrocks into a rock like quartzite, of a black or bluishcolour. These tracts of paroptetic rocks are almost invari-ably margined by joint or fault lines, and traversed byothers ; as if the action was not so much due to heat given Fi£. 6. OrctrvitcmeOahbro + +, Felstcne AA* BakedShale v.: \ Tu/r Shalef&GritsAlluvuun- Map of Baked Rocks round vent of eruption, Owenduff, County Wexford. off from the mass of eruptive rock as to the steam, gases,and such like products of vulcanicity given off during thetime the eruptions were taking place, which percolatedthrough the adjoining rocks and altered them, prior to thetime that the present granitic rocks consolidated. Thatan alteration similar to that now described, and due solely Metamorphic Rocks. 185 to the gases and suchlike products of vulcanicity can takeplace, is proved in various localities where tracts of similarparoptetic rocks occur, although there are no protrusions oferuptive rocks associated with them. * The vents or pas-sages of the Plutonic outburst are also found higher up inthe formation among the lower rocks of the Ballymoneyseries. Here, since many of the altered rocks were origi-nally felspathic and basic tuffs or tuffose
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