Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/728

624 "Grey and dark shales, with bands of flag- Stage C. stone, clay-iroastone, and cemcnt- Yoredale Series. stones. Fossils abundant, Goniatites, . Posidonomya Becheri, &c 600 Stage B Carboniferous Limestone. In the above series we have, in stage E, clearly the representa- tives of the Gannister Beds with their characteristically marine fauna, in addition to the Millstone Grit. It is somewhat doubtful where the line between these two divisions should be drawn ; but this is of little moment so long as we can be certain that they are both there. The representatives of the [Middle] Coal-measures (stage F) have been entirely removed by denudation. 2. The Tyrone Coal-field. — This is the most important coal-field in Ireland, as in it the Coal-measures (stage F) are developed to an extent nowhere else equalled, and contain numerous beds of bitumi- nous coal (see Section, fig. 2, p. 618). The Lower, or Gannister beds are very largely developed, while on the other hand the Millstone Grit and Yoredale beds are comparatively unimportant as regards their vertical thickness. An admirable Eeport on the structure of this coal-field was drawn up in 1829 by Sir R. Griffith for the Royal Dublin Society ; and since then the Geological Survey of the district has nearly been completed, and a memoir thereon by Mr. Hardman will shortly be issued. The coal-field itself forms a triangular area, bounded along the north by a large upcast fault, bringing to the surface the Carboniferous Limestone, along the east by the Triassic formation (below which the Carboniferous beds extend), and along the south by the natural outcrop of the strata. At Drumglas Colliery the lowest seam has been worked, its position being near the base of the Lower Coal- measures (stage E). A synopsis of the Carboniferous series by Mr. E. T. Hardman is published in the Trans, of the British Association for 1874, from which the following section is condensed *. Section of the Tyrone Coal-field near Dungannon (fig. 2). Feet. Stage F. Coal-measures. — Sandstones, shales, and clays, with eight or ten coal-seams. Fossils : fish, Anthracosia, Lingula squamosa, &c. (Coal island), plants, ferns, &c about 930 Stage E. Gannister Beds. — Sandstones, shales, &c., and two or three workable coals (Crenagh and Drumglas). Fossils: fish-remains, Orthoceras, Goniatites, Productus, and Lingular about 1000 Stage D. — Millstone Grit. — Coarse grits below the Drumglas Coal ,, 200 Stage C. Yoredale Beds. — Black shales with bands of limestone, sand- stone, and clay-ironstone nodules 600 Stage B. Carboniferous Limestone (Dungannon). (1874). t Lingula squamosa occurs in shales over the " Crenagh Coal," which is high up in the Lower Coal-measures (see Geological-Survey maps, 6-inch scale, No. 47, co. Tyrone) ; also above the Yard and Belteboy seams in stage F.
 * "On the Structure of the Tyrone Coal-field," Bep. B. A. Trans. Sect. p. 77