﻿416 ME. L. EICHAKDSON ON THE RHJETIC AND [Aug. I905, 



PL hettangiensis, and Lima valoniensis being especially abundant. 

 A stratum which probably represents the Sun-Bed completes the 

 equivalent of the White Lias of the Bath district : the representa- 

 tive of Bed A of the Lavernock and Barry sections is only found over 

 a restricted area, and probably indicates a deepening of the sea 

 in this neighbourhood, caused by renewed earth-pressures. 



During the period when the White-Lias limestones and shales 

 (A & B, Lavernock) were being deposited, the Gotham Marble in 

 certain localities was hardened, broken up, and cemented into a 

 conglomerate — for example, at Sedbury Cliff, near Chepstow. As 

 remarked by Dr. Arthur Yaughan, 



' The time occupied by the hardening of the Cotham layer [at Sedbury Cliff], 

 its destruction, and subsequent cementation into a conglomerate may be con- 

 sidered to correspond roughly to the time cf deposition of the White Lias in 

 the areas on the south and east.' (Quart. Journ. Geol. Soc. vol. lix, 1903, 

 p. 397.) 



It is interesting to observe also that the same author thought 

 that 



' At Sedbury Cliff the deposition of the Cotham Marble must have been 

 succeeded by an elevation of the floor, which produced the breaking-up of the 

 Cotham-Marble layer in situ? (Ibid. p. 398.) 



At the time when the Lower Liassic 'Paper-Shales' were formed, 

 the bathymetric conditions were about the same in the West of 

 En eland. 



In the description of the various sections in this shire, reference 

 has been made to the stratigraphical position of the White Lias, and 

 it will have been noticed that this deposit is considered to come 

 above the Cotham Marble. Eecent work accomplished by several 

 geologists in the Bristol district has demonstrated that such is its 

 correct stratigraphical position. 



As long ago as 1864, Bristow & Etheridge, in their account of 

 the Ehsetic beds at Penarth, referred to i bands of limestone and 

 indurated marl (in brown shale),' which they considered might be 

 i equivalent to the " White Lias." . . . The place of the Cotham 

 Marble (not observed here)/ they added, ' is at the base of this 

 group of beds.' (Geol. Mag. vol. i, p. 237.) 



It has been remarked recently that the denomination White 

 Lias is a useful stratigraphical term for the Upper Elastic 

 Beds in the region extending southwards from Bath (Geol. Mag. 

 1905, p. 79). 



Since the term Upper Eh a? tic has been applied by different 

 authors to obviously non-contemporaneous strata, it is desirable to 

 define exactly to what beds it has been applied in the present paper. 

 The 'L T pper Bhsetic' of my records of the sections in North- West 

 Gloucestershire, and those at Wood Norton (near Evesham), Sedbury 

 Cliff (near Chepstow), and elsewhere, is not the equivalent of the 

 White Lias. 



