Vol. 67.] WEST, MID, AND EAST SOMERSET. 73 



Dr. J. E. Mark expressed the desire that names ending in ' ian ' 1 

 should, so far as possible, be confined to those larger divisions 

 which in the nomenclature of the International Geological Congress 

 were called ' series.' As a teacher, he would suggest that less 

 confusion would be introduced if the Author adopted the term 

 ' Rhsetian ' for what he called ' Rhaetic,' and used the terms 

 4 Somerset Beds ' and ' Lilstock-Sully Beds ' for what appeared as 

 * Somersetian ' and ' Rhaetian ' in his stratigraphical table. Each 

 of the two last-named divisions included only about 60 feet of rock, 

 and they were, therefore, hardly ' series ' in the accepted sense of 

 that term. 



Dr. Sxrahan, while expressing his sense of the value of the 

 Author's highly detailed examination of Rhaetic sections, still 

 found himself unable to accept the definition of the Rhaetic base 

 given in this paper. Previously to the re-survey of South Wales 

 the Tea-green Marls had been included in the Rhaetic. They passed, 

 however, so imperceptibly down into the underlying Red Marls, 

 that it was obviously impossible to separate them with precision. 

 On the other hand, there existed between these green beds and 

 the overlying Black Shales a well-marked plane of separation which 

 was recognizable over a large area in England and Wales. No fossils, 

 beyond some remains of fishes and an oyster, were known to occur 

 below this plane in South Wales, whereas a Rhaetic fauna abounded 

 above it — facts which, taken in conjunction with the occurrence of 

 a conglomeratic Bone-Bed resting on the plane, indicated a sudden 

 invasion of the sea. Subsequently to the re-survey the Author 

 recorded Rhaetic fossils from below this plane, the account of their 

 occurrence, however, being such as to leave him (the speaker) 

 under the impression that they had been found on the top of the 

 green beds, not in them. If, as the Author now again maintained, 

 they occurred in the green beds, the fact would be interesting as 

 showing that a prevalence of estuarine conditions enabled some of 

 the Rhaetic molluscs to enter the region before the general incursion 

 of the Rhaetic fauna. How nice was the balance between estuarine 

 and open-sea conditions was indicated by a temporary recurrence 

 of sediments of Keuper-Marl type in the Upper Rhaetic. The 

 appearance, however, in the green beds of a few forerunners of 

 the Rhaetic fauna did not convince the speaker that a well-marked 

 stratigraphical and palaeontological horizon should be abandoned in 



1 [The following was the classification suggested, with the exception of two 

 alterations: the replacement of the term Westbury Beds bv Cotham. 

 Beds (III), and that of Lilstock Beds by Westbury Beds (IV):— 



Lias. Hettangian. Ostrea Beds, etc. 



Watchet Beds (« Marly Beds of the White 



Lias '). 

 i Somersetian. \ TT T ' . -r> n /tttu-«. T • \ 



-p \ H- Langport Beds (White Lias proper). 



HII^TIC. ^ TTT nnf i, am T. pflo /TTtwm,,. P.I-,«.Hn1 



Cotbam Beds (Upper Rbcetic). 

 [ -o . . • J IV. Westbury Beds (Black Shales). 



» V. Sully Beds (Fossiliferous Grey Marls). 



Keuper. Keuperian. Tea-green and Grey Marls. Bed Marls. 



" L. R., February 16th, 1911.] 



