Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/718

614 been able to ascertain, the term "Coal-measures" has come to be applied to all the beds from the top of the Limestone up to the coal-bearing measures of the Leinster Coal-field and of the corresponding beds of Kerry, Limerick, and Clare. The consequence is that it has sometimes been supposed that the coal-bearing districts of the south of Ireland are much more extensive than is actually the case. As far as the maps of the Geological Survey are concerned, we are now taking steps to give to the public a truer idea of the actual limits of the coal-bearing strata, and also to correlate with the British series the strata between them and the Limestone. Mr. Hardman has nearly completed a resurvey of the coal-districts of Carlow, Kilkenny, and Tipperary, resulting in a more accurate and detailed representation of the different divisions; and I hope a similar revision will ultimately be extended to that large area in the south-west occupied by similar beds, with very little true Coal-measures at all, but which has been described only recently as "one of the largest coal-fields in the British Islands."

Notwithstanding that the term "Coal-measures" has been applied to all the beds above alluded to in the publications of the Geological Survey as well as of amateur geologists, the late Director of the Irish Survey, Professor Jukes, has left on record his opinion that the lower portion of them, including the shales and flags immediately over the Limestone, are in reality the representatives of the Millstone-Grit series of England. Thus, in the Explanatory Memoir to sheet 137 of the maps of the Geological Survey, he says:—"Doubtless the whole of the Coal-measure series of Central Ireland is contemporaneous with the lower part only of that of Central England, including the Millstone Grit in that lower part."

I have reason to believe, from a conversation I have had with the father of Irish geology himself, Sir R. Griffith, that he shares the same opinion; and if there had been room for doubt on the subject on other grounds, this doubt must have been dispelled upon the identification in the Leinster Coal-field of that peculiar and important member of the Carboniferous series, namely the "Lower Coal-measures" or "Gannister Beds," which, in the north of England, overlies the Millstone Grit, and contains the expiring representatives of the marine fauna of the Lower Carboniferous series as hitherto constituted.

The additions which are now being made to the maps of the Geological Survey of the Leinster and Minister coal-fields will be at once understood when it is stated that instead of one formation, re- presented by one shade of dark colour, and included under the general term of "Coal-measures," we are tracing out and distinguishing representatives of four divisions, viz.:—1. Yoredale Beds; 2. Millstone Grit; 3. Gannister Beds; and 4. the Middle Coal-measures of the British series. The changes thus effected will have, at