Yol. 67 .] WEST, MID, AND EAST SOMERSET. 3 



(e) That the marly beds above the White Lias proper, which correspond 

 to similar marly beds at Lavernock (where they were provisionally 

 grouped with the equivalent of the White Lias pi'oper), are worthy of 

 separation and distinct designation. 



Indeed, it has become increasingly evident that, in order to be 

 able to set forth, clearly the changes in lithic structure which the 

 lihaetic Series undergoes from place to place, and to convey to the 

 palaeontologist a knowledge of the horizons whence the fossils with 

 which he may be dealing came, certain new stratigraphical terms are 

 •essential. These are discussed in a later portion of this paper. 



(i) Geographical extent of the Bhsetic Series. — The 

 Bhsetic beds have a greater superficial extent in this county than 

 in any other, and their distribution is best seen upon reference to 

 the Geological Survey maps. 



(ii) On the lower and upper limits of the Bhsetic 

 Series. — In the Midland Counties the line of demarcation between 

 the Keuper and the Bhaetic is sharply defined * : the Tea- 

 green Marls are succeeded suddenly by the well-known Black 

 Shales. But in "West Somerset, and in the Lavernock district 

 on the opposite Glamorgan coast, there are, between the Tea- 

 green Marls and the Black Shales, 'Grey Marls': real 

 4 passage-beds,' for dark bands occur in them at more than one 

 horizon and in their uppermost 14 feet or so — as Prof. Boyd 

 Dawkins long ago pointed out 2 — characteristic Bhastic fossils make 

 their appearance. For these top 14 feet of fossiliferous Grey 

 Marls I have suggested the name of ' Sully Beds.' 3 



Although the gap between the Tea-green Marls and the Black 

 Shales on the Bristol-Channel littoral is thus to a considerable 

 extent bridged over by the intervention of the Grey Marls 4 and 

 Sully Beds, there is still a non- sequence at the top — between the 

 Sully Beds and the overlying Black Shales. The upper surface 

 of the Sully Beds at Lavernock was deeply channelled before the 

 deposition of the Black Shales 5 ; while, both at St. Mary's- Well 

 Bay (Sully) and at Lilstock, the top-layer of the Sully Beds is a 

 thin band of impure limestone, practically made up of specimens of 

 Pteria contorta, thus betokening slow formation. It is also inter- 

 esting to note that other portions of the Sully Beds afford evidence 



1 E. Wilson, Q. J. G. S. vol. xxxviii (1882) p. 455 ; and Proc. Bristol Nat. 

 Soc. ser. 3, vol. vii (1893-94) pp. 218 et seqq. 



2 Q. J. G. S. vol. xx (1864) pp. 397-98. 



3 Ibid, vol. lxi (1905) p. 386. 



1 In this paper the term ' Grey Marls' means those deposits, less the fossi- 

 liferous top-portion or Sully Beds. The term ' Grey and Tea-green Marls' 

 means the Grey Marls, as thus defined, plus the Tea-green Marls, and in the 

 record of a section indicates that I think that both those deposits in part or 

 wholly are represented ; while the usage of the term ' Tea-green Marls ' alone 

 implies that I think that there are no Grey Marls represented— only Tea-green 

 Marls. 



5 Q. J. G. S. vol. lxi (1905) fig. 1, p. 390. 



b2 



