72 SECTIONAL ADDRESSES. 



pseudobilinque beds aud certain underlying shales (' Pendleside shales ') 

 being absent. 



Sibly ^^ describes a case near Youlgreave where the ' Pendleside shales ' 

 with Posidoniella Icevis rest on D.^, the Cyathaxonia beds, D.„ being absent ; 

 Wedd ^^ a similar case near Bridgetown, Derbyshire. Mr. Hudson informs 

 me that in the Knoll region of Cracow the upper Bowland shale rests 

 unconformably on the Knoll limestones, which were subject to uplift and 

 denudation prior to the deposition of the lower E beds. 



The great post-Avonian unconformity at the base of the Millstone Grit 

 is described more fully in the sequel. 



Note. — The nomenclature of the rocks of the Pendle Hill area is very 

 confusing to those unfamiliar with the district. The Pendleside 

 group of Hind and Howe (1897) originally included all the strata 

 between the Mountain Limestone and Millstone Grit, and was con- 

 sidered to be all of Upper C!arboniferous age. Subsequently Hind 

 relegated the lower part of his ' Pendleside series ' (the ' shales with 

 limestone ' of the Survey and the Worston shale of Parkinson) to the 

 D beds, leaving the Pendleside limestone and overlying shales, the 

 Bowland shale of Phillips, in his ' Pendleside group.' He also included 

 in it the shales overlying the Pendle top grit, which later work has 

 shown to be Lancastrian. It is clear from the above account that, 

 although the terms ' Pendleside ' and ' Pendleside group ' are frequently 

 employed as roughly equivalent to Phillips' Bowland shale, they lack 

 definiteness and there is little to justify their retention. Mr. Bisat ^^ 

 and Dr. Parkinson^* clearly show that the terms, as indicating a time 

 division, had better be drojaped. 



The grits of the Pendleside section are also confusing, and in 

 hopes of making things clearer I have carried on the section in 

 Table II. up to the Kinderscout grit from information supplied by 

 Dr. Parkinson. 



Piping or Pot-holing under Subaerial Conditions on Levels of 



Unconformity. 



Several interesting examples liave been described : — 



(a) Dixon describes^" very remarkable cases from If ton, Monmouth, 

 where the S beds below the Millstone Grit are worn into steep-sided 

 channels and cavities, some of imknown depth filled with sandstone and 

 shale. 



(b) In the Forest of Dean Sibly describes^" piping of the Carboniferous 

 Limestone by Coal Measure sandstone at Kuardean. 



(c) Dixon alludes 2^^ to piping at Llanmarch Dingle, near Brynmawr, 

 in the north-eastern portion of the South Wales coalfield. Here grit fills 

 holes in the Carboniferous Limestone. 



^^tQ.J.0.8., vol. Ixiv. (1908), p. 63. 



1" iV. Derby Memoir, p. 35. 



1' Proc. Yorks Oeol. Soc, vol. xx., pt. 1 (1923-4), p. 45. 



i« Q.J.G.S., vol. Ixxxii. (1926), p. 223. 



" Geol. Mag., vol. Iviii. (1921), p. 157. 



=" Ibid.,*T)eo. vi., vol. v. (1918), p. 26. 



" g.J.G.8., vol. Ixxiii. (1917), pp. 161-2. 



