Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/860

720 720 PKOE. E. HTJIX ON THE DINGLE BEDS AND it becomes attenuated, and ultimately terminates against the flanks of the old granite ridge, where it is conformably overlapped and dis- appears beneath the Carboniferous Limestone, which, in turn, abuts on the same granitic ridge at Gores Bridge. Throughout this tract the Old Red Sandstone consists of dull, reddish-brown, rather soft sandstone, often pebbly, and sometimes supported by thick masses of breccia and conglomerate of quartz, jasper, trap, and Lower Silurian grit. The upper beds contain bands of reddish shale, and the whole series attains in Co. Waterford a thickness of about 3200 feet*. The formation, indeed, in its usual condition, bears a strong resemblance to the " Pebble-beds " of the New Red Sandstone of Lancashire and Cheshire ; and, on the other hand, has but a faint resemblance to the " Dingle beds" and Glen- gariff-grit series." The contrast has long ago been pointed out by the late Mr. John Kelly, E.G.S., in the following passage, which I quote in preference to using language of my own : — " The Old Red Sandstone has two prominent points of character which, in all parts of Ireland, stand out in relief and make it a rock which cannot be mistaken for any other. The first is a thick band of conglomerate at its base, which generally contains quartz, jasper, and other pebbles. The second that this conglomerate always lies uncon- formably on the inferior rock. The other characteristics are that the lower part of it is usually of a red colour ; it passes upwards into yellow ; but both are comparatively soft, and easily split for economic use into rudely rectangular blocks, a circumstance quite at variance with, and distinguishing it from, the Silurian grits [meaning Glen- gariff grits, &c], which are so much affected by cleavage and so hard, that the blocks are quite refractory under the wedge, hammer, or chisel, and cannot be worked satisfactorily for building- purposes "f. The upper portion of the formation consists of pale yellow and greenish sandstones and shales, sometimes containing pebbly beds, often rippled and flaggy, and containing remains of plants, fresh- water bivalves, and fish, such as Boihriolepis (Dendroclus), Goccos- teus, Pterichthys, Glyptolepis elegans. Palseontologically, this is the most interesting and important member of the whole group,' and is, in all probability, the equivalent of that part of the Upper Old Red of Scotland containing the sandstones of Dura Den, with Holoptycliius and other fishes, to which the Yellow Sandstone of the south of Ire- land bears sometimes, curiously enough, a strong resemblance. Professor Geikie has suggested that the Dingle beds or Glengariff Grits may be the representatives of the " Lower Old Red Sandstone " of Scotland (" Old Red Sandstone of "Western Europe," parti. Trans. Roy. Soc. Edinb. 1878). If this be so, then they would be the marine representatives of lacustrine deposits. Both are unconform- ably overlain by (Upper) Old Red Conglomerate and Sandstone. t " Extracts" which were intended to beapplied to Sir R. Griffith's Geological Map, published in ' Atlantis,' January 1859.
 * " Explanation " to sheets 167, 168, &c. of the Geol. Survey Maps, p. 15.