﻿414 MR. L. KICHARDSON ON THE 1ULZETIC AND [Aug. I905, 



Keuper. No mention is made in the Geological-Survey publications 

 of the abundant occurrence of Ostrea in the 'Tea-Green Marls' at 

 St. Mary's-Well Bay, Sully : it is observed that these marls 



' are distinguished from the Kheetic formation by the fact that they have 

 hitherto proved to be totally unfossiliferous in South Wales, except for the 

 occurrence of a bone-bed at Goldcliff.' 1 



This statement, however, is modified in a subsequent part of the 

 same memoir, 2 but the same classification is adhered to. Although 

 I have been compelled, from the palseontological evidence, to suggest 

 that the Sully Beds be classed with the Rheetic, I nevertheless quite 

 agree that the line of demarcation between Keuper and Ehsetic 

 decided upon by the officers of the Geological Survey is the most 

 satisfactory for their purpose, because it is then possible to indicate 

 on the map where the lithic change takes place. 3 



Renewed earth-movements occurred before the deposition of the 

 Rhsetic Black Shales, and brought about conditions suitable for a 

 slight erosion of the uppermost stratum of the Sully Beds. In the 

 Penarth-Lavernock section, indications of such an erosion are most 

 apparent. 



I would here direct attention to the fact that Mr. E. T. Howard, 

 P.G.S., is of opinion that 



' in South Wales, at least, there was a slight upheaval instead of a sub- 

 sidence just at the close of the Trias Period (immediately preceding the 

 subsidence of Rheetic and Liassic times, about which the evidence is indis- 

 putable). We see at once that the newly-formed Trias beds might be raised 

 into dry land, and immediately attacked by the various agents of denudation.' 4 



V. Conditions op Deposition op the Rustic Black Shales. 



So far as is known at present, while the Black Shales or sand- 

 stones containing Pteria (Avicula) contorta were being deposited in the 

 Glamorganshire district, no appreciable earth-movements occurred. 



1 ' The Geology of the South Wales Coalfield : Pt. i— The Country around 

 Newport, Mon.' Mem. Geol. Surv. 1899, p. 70. 



2 Ibid. Pt. iii— ' The Country around Cardiff' 1902, p. 41. 



3 Since this paper was written, that dealing with the Ehgetic rocks of 

 Monmouthshire has been communicated to the Geological Society. In the 

 discussion which ensued (Quart. Journ. Geol. Soc. vol. lxi, 1905, p. 384) 

 Mr. Strahan said that he had been unable to identify the « Grey Marls ' of 

 Etheridge, and doubted whether any such subdivision of the ' Tea-Green Marls ' 

 could be made. The palaeontological evidence set forth in the present paper 

 requires such a division ; but, of course, the actual line of demarcation between 

 the Sully Beds and the ' Tea-Green Marls ' must be more or less arbitrary, and 

 governed solely by paleeontological considerations. Mr. Strahan also doubted 

 whether there was any overlapping of the ' Tea-Green Marls' by the Avicula- 

 contorta Shales, and remarked that they varied but little in thickness over 

 the whole region. According to the Geological-Survey publications, the 

 ' Tea-Green Marls ' at Lis-Werry measure 13 feet (' Geology of the South 

 Wales Coalfield : Pt. i— The Country around Newport, Mon.' Mem. Geol. 

 Surv. 1899, p. 74) and at Lavernock 44 1 feet (ibid. Pt. iii — ' The Country 

 around Cardiff' 1902, p. 54)— a difference of 31.J feet. 



4 Trans. Cardiff Nat. Soc. vol. xxix (1896-97) pp. 65-66. 



