C— GEOLOGY. 7:i 



{(l) Piping occurs in Z beds at Pendine^'^ bel?»w the conglomeratic base 

 of the S beds, and at Haroldston St. Issell-^ Millstone Grit pipes into 

 limestone of a low S horizon. At West Williamstown"* the case is some- 

 what different, as here the material forming pipes in the C«>m??"a-oolite(C,) 

 is C, mudstone, and consequently does not imply any considerable break. 

 It was found, however, that the upper part of the CVf;(?/«i«-oolite is 

 missing, and the inference was drawn that the case at West Williamstown 

 is analogous to the others, the emergence, though brief, being sufficient to 

 bring the limestone within reach of subaerial agencies. 



(e) Greenly describes ^^ cases in Anglesey where at several levels in D., 

 beds of sandstone pipe into the limestone. 



(/) In the West Cumberland area Edmonds"'** and Dixon ^^ describe 

 contemporaneous pot-holes recurring at several horizons intho Fourth lime- 

 stone (Di to D3). They are mainly cylindrical, with an average diameter 

 of 2 feet and depth of 4-6 feet. They widen oiit rapidly at the top and 

 are filled with mudstone, sandstone or rubbly limestone. They point to 

 repeated intervals during which subsidence and deposition of limestone 

 were interrupted by elevation above sea-level and contemporaneous 

 erosion. 



(g) Near Ingleton pot-holes in D, limestone have been recognised by 

 Dixon.2* 



(h) The pits in the pitted D^ limestone of Gower^® are also of the 

 character of contemporaneous pot-holing. 



Phasal Equivalents oJ the Avonian. 



In his most suggestive report presented at the Winnipeg Meeting of 

 the British Association in 19(j9 Vaughan recognised three phasal equiva- 

 lents, and introduced, though without defining, the following terms to 

 express them : — 



1. Standard fauna. 



2. Zaj)hrentid and Cyathaxonid phase. 



3. Modiola and Posidonomya phase and other shallow-water deposits. 

 He regarded the ' standard fauna ' as indicating the greatest depth of 



water, and the Modiola and Posidonomya phase the least. 



1. Standard -phase. — This type of deposit, which is mainly calcareous 

 in character, is seen in most of Z, y, S.j and Dj in the Avon section and 

 in the Mendips also in C, and C,. In the North-west Province and in the 

 Midlands D, and D.^ are standard phase and in N.W. Yorkshire and 

 Westmorland S and the whole of Dj and Dj. 



2. Zaphrentid and Cyathaxonid phase or fauna. — Dixon gives a clear 

 statement of the sense in which he uses this expression. He describes the 



"^ Haverfordioest Memoir, p. 142. 



23 Ibid., p. 161. 



'*Ibid., p. 142. 



'^Oeol.Mag., Dec. iv., vol. vii.( 1900), pp. 20-24, and Anglesey Memoir, pp.612-16. 



20 Ibid., vol. lix. (1922), pp. 120-1. 



■^' Summary of Progress for 1921, pp. 53-4. 



•;« Q.J.G.S.. vol. Ixxx. (1924), p. 215. 



23 Figured Q.J.G.S., vol. Ixvii. (1911), pi. Ixxxviii., fig. 1. 



