Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/723

Rh OF THE CARBONIFEROUS SERIES. 619 The Lower Limestone here rests on the granite of Leinster, so that Stage A is not represented here. It will be unnecessary for me to give a detailed description of the range, and order of succession, of the Carboniferous beds in this district, after the numerous publications already in existence treating of this, the most important coal-field in the south of Ire- land * ; and I shall therefore confine my observations to those points which concern my argument, namely the upper limit of the truly marine fauna, and its representative horizon amongst the British series. The shales overlying the Carboniferous Limestone are admitted by all observers to be essentially marine, the large number of fossils which have been collected both by Griffith and the officers of the Geological Survey having placed this beyond question ; of these Posidonomya Becheri is perhaps the most characteristic form. AYe have only to compare the lists of forms obtained from these beds in the south of Ireland with those from the Yoredale Shales of the north of England to see that the fossils of the one are representative of, if not identical with, those of the other, and that both are of marine origin f. Here we find Goniatites, Bellerophon, Euompha- lus, Avieulopecten, and Posidonomya, the successors of the forms which flourished more vigorously in the sea of the preceding period. Physical break between the Limestone and Yoredale Shales. — The line of demarcation between the Carboniferous Limestone and over- lying shales is more than usually decisive around the Leinster Coal- field. Mr. Hardman, of the Geological Survey, assures me that there is not only an abrupt change in the mineral character of the beds, but that this is accompanied by a physical break or discordance. This abrupt change is general over the southern districts of Ire- land t. In fact the upper beds of the limestone have in this region un- dergone a species of pseudomorphism, and are largely converted into chert; and my colleague, Mr. Hardman, agrees with me that this process has taken place before the deposition of the Yoredale Shales, and is a consequence of certain physical changes which took place over the bed of the sea. To this subject I hope to return on another occasion ; but I wish here to observe that the Yoredale Beds of Ireland are more intimately associated with the Millstone Grit and Gannister Beds than with the Carboniferous Limestone — which by Sir R. Griffith (1814), accompanied by an engraved map and sections ; Ex- planations of the sheets 128 and 142 of the maps of the Geological Survey of Ireland, by Messrs. Jukes, Kinahan, and O'Kelly (1859) ; " The Leinster Coal- field," by J. M'C. Meadows, Journ. Roy. Geol. Soc. of Ireland, vol. iv. part i. (1873-4) ; ' The Coal-fields of Great Britain,' 3rd edit. p. 300 et seq. (1873). t For instance, compare the list given by Jukes and Geikie, ' Manual of Geo- logy,' 3rd edit. p. 592, with those of the late Mr. Salter from the corresponding 6eries in Lancashire, " Geology of the Country around Oldham," Mem. Geol. Survey, Appendix, p. 59 ; and " Geology of Stockport, Macclesfield, &c," ibid. p. 92. Expl. to sheet 46, N.W. p. 20.
 * The following are the principal : — 'Report upon the Leinster Coal-district,'
 * See Explanation to sheet 163 &c. of the Geological-Survey Maps, p. 14 ; also