THE lar.r.Tic rocks at tylle hill. MV 



Acrodus inlnimHS^ Sanriclitliys ariiminatus^ and Gi/roUpis Alherlu. 

 I consider tlie limestones and shales i to a homotaxial with the 

 shales and nodular limestones containing Kstherice which wo find 

 in the ^Midland district directly overlying the Avkula-contorta 

 shales. These beds I designate " Upper lihajtic,"' a term which 

 seems preferable to that of " White Lias '' as applied to rocks which, 

 in a geological sense, are not Lias at all. 



Auotlier feature which the Pylle-Hill section displays very clearly 

 is the intimate connexion between the " Tea-green Marls " and the 

 underlying lied Marls of the Upper Keuper. Whilst there is a 

 sharp j)hysical line of demarcation, as well as a total difference in 

 mineral character, between the " Tea-green Marls " and the black 

 shales of the Avicula-contorta series, the " Tea-green Marls " are 

 themselves seen to blend insensibly into the underlying lied Marls 

 of the Keuper. This section, therefore, like so many others at the 

 same horizon, both in the West of England and in the Midland 

 Counties, indicates that the '* Tea-green Marls " belong to the 

 Keuper and not to the liha^tic series, and also that they cannot 

 properly be looked upon as passage-beds between those two forma- 

 tions. The authors who first determined Rhastic rocks in England 

 — Ml'. Charles Moore and Dr. Thomas Wright — took this view ; 

 and drew the dividing line between the Rhsetic and the Trias at 

 the base of the Avicula-contorta shales, classing the underlying 

 greenish-grey marls with the Keuper *. In his original description 

 of the section at Garden Cliff, Westbury-on- Severn, Mr. E. Etheridge 

 placed the " Tea-green Marls " in the Hhsetic series t, but in 1871 

 he had come to consider these beds as more properly associated 

 with the Keuper J. The Geological-Survey authorities, although 

 admitting the fact that the " Tea-green Marls " graduate down into 

 the variegated marls of the Upper Keuper, have nevertheless been 

 in the habit of classing these beds with the overlying black Paper 

 Shales, and the " White Lias " under the common term " Penarthor 

 Rhaetic beds '" §. Mr. H. B. Woodward advocates this method 

 of classification, partly on the ground that on the maps of the Geolo- 

 gical Survey it was found more practicable to draw the line between 

 the Hhictic and the Keuper beds at the base of the grey marls, and 

 partly because in certain E,ha)tic sections, such as those near Axmouth 

 and Watchet, there are appearances of a transition, for " bands of 

 very dark, if not black, marl alternate with pale gre}- and buff marls, 

 above the lied Marls of the Keuper " |j. It is also alleged that the 



* C. Moore, Quart. Journ. Geol. Soc. vol. xvii. (1861) p. 403 : T. Wright, 

 ibid. vol. xvi. (1860) pp. 378, 380, 383, and Pal. Soc. Monogr. ' Lias Ammo- 

 nites' (1880), p. 165, fig. 13. 



t ' Ou the Rhaitic or Avicula-contorta beds at Garden Cliff, Westbury- 

 iipon-Severn,' Proc. Cottesw. Nat. Field Club, vol. iii. (1865) p. 218. 



\ ' On the Physical Structure and Organic Eemains of ihe Penarth (Ehaetic) 

 Beds of Penarth and Lavernock, with a description of the Westbury-on-Severn 

 Section,' Trans. Cardiff Nat. Soc. vol. iii. (1870-71) p. 39. 



§ H. B. Woodward. Mem. Geol. Surv., 'Geol. of East Somerset and the 

 Bristol Coal-Fields,' p'. 6t). 



II Id. ' Geology of England and Wales,' 2nd ed. (1887), pp. 243-246 ; and 

 ' Notes on the Rliaetic Beds and Lias of Glamorganshire,' Proc. Geol. Assoc, 

 vol. X. (1888) p. 529. 



Q.J.G.S. No. 188. 2q 



