Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/730

626 62Q EDWARD HULL ON THE CLASSIFICATION On a former occasion I have endeavoured to explain the origin of the phenomena presented in this coal-district *. Here we find the Carboniferous Limestone represented by only a few feet of that material, its place being taken by sedimentary, or mechanical, deposits. It is exactly a parallel case with that which occurs in North Britain. In the Clyde basin, as is well known, the Carboni- ferous Limestone (as such) is represented by only a few thin bands, which, however, swell out as we proceed southwards, until in Derbyshire the formation is a solid mass of limestone at least 5000 feet in thickness f. The changes which took place in Britain during the period of the Carboniferous Limestone and subsequently, had also their counterpart in Ireland. Thus we find, in proceeding northwards from the central plain, the beds of limestone, which there attain a thickness of 2500 feet, begin to change their charac- ters. In Fermanagh, Tyrone, and Armagh the " Calp," or Middle Limestone, has passed into massive sandstones and beds of shale with very thin coal-seams ; and the Lower Limestone is largely mixed with similar beds. Still further north the limestone dimi- nishes in thickness, till on the shores of Antrim and in Deny the calcareous beds seem on the point of disappearing. Part III. English Carboniferous Districts. Having now completed our survey of the Irish Carboniferous districts, I propose briefly to extend it over the British area, in order to point out the equivalent stages. A brief description of a few typical sections will probably be considered sufficient — as so much has been written on the subject already. Adopting the lettering of the successive stages, as already given in the Table (pp. 615, 616) of the British Carboniferous Series, I shall commence with South Lancashire, which may be taken as the typical district, owing to the magnificent development of all the stages from the Mountain Limestone upwards. (1) South- Lancashire District. Our knowledge of the succession of the beds in this district is largely owing to the labours of Mr. E. W. Binney, F.R.S. ; and the mode of clasification adopted by the Geological Survey differs but slightly from his. It is as follows : — details of the above are treated in the author's paper " On the Eelative Distribu- tion of the Calcareous and Sedimentary Strata of the Carboniferous Period," Quart. Journ. Geol. Soc. vol. xviii. p. 127. t Some recent authors have placed the thickness of the Derbyshire limestone at only half this amount; but the measured sections published by the Geological Survey place the thickness, as here stated, almost beyond doubt,
 * 'iOn the Geological Age of the Ballycastle Coal-field," stipra cit. The