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 : — 



* 'iOn the Geological Age of the Ballycastle Coal-field," stipra cit. The 

 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, 



