396 MR. A. VAUGHAN" ON THE LOWEST BEDS [Aug. I903. 



32. The Lowest Beds of the Lower Lias at Sedbtjry Clife. By 

 Arthur Vattghan, Esq., B.A., B.Sc.. F.G.S. (Read June 24th, 

 1903.) 



The two chief points of interest in the Lower Lias of Sedbury Cliff, 

 which I examined in company with Mr. L. Richardson, are, 

 firstly, the relation of the basal conglomerate to the Cotham Marble 

 and White Lias of neighbouring districts ; and, secondly, the 

 examination of the faunal sequence, with a view to testing the 

 absolute value of ammonite-zones. 



1. The Conglomerate. 



This is composed of fragments of a very compact, lithographic, 

 argillaceous limestone, which exhibits well-marked conchoidal 

 fracture. The large fragments are invariably tabular and lie 

 horizontally, their vertical dimension being small compared with 

 their horizontal extent ; all of them show internal, horizontal bands 

 of colour which may undoubtedly be considered to have existed in 

 the original rock-layer from which the fragments were broken. 

 The smaller fragments lie in all directions, and many of them are 

 rounded ; they almost invariably exhibit an outer, more deeply 

 stained shell, the colour of which shades off inward quite uniformly 

 and imperceptibly. There can be little doubt that this staining has 

 been produced subsequently to the breaking and rolling of the 

 fragments, and, most probably, subsequently to their cementation 

 into a conglomerate. 



That the fragments of the conglomerate once formed part of 

 a layer exactly similar to the true Cotham Marble of the Bristol 

 and Sodbury areas, is almost without question, since they agree 

 absolutely in lithological characters with specimens of that rock, 

 though I have noticed no fragments which show the peculiar 

 arborescent markings. It is, however, important to notice that the 

 arborescent marking, though peculiar, does not form an essential 

 character of the Cotham-Marble layer, being very commonly absent 1 ; 

 whereas some form of undulating, horizontal banding, especially 

 near the base of the layer, is almost invariable. 



The resemblance of this conglomerate to the so-called ' False- 

 Cotham ' 2 is still more striking, for the shape, colouring, and 

 irregular lie of the thin, tabular fragments are identical in the 

 two rocks. The main differences are that, in the conglomerate, 

 the smaller fragments are frequently rounded, and the matrix is 

 dissimilar in character from the fragments which it cements. In 

 ' False-Cotham ' the fragments are almost invariably tabular, very 



1 See Beeby Thompson, ' Landscape Marble ' Quart. Journ. Geol. Soc. vol. 1 

 (1894) p. 399. 



2 The term ■ False-Cotham ' was, I believe, first employed by Mr. J. Parsons, 

 B.Sc, F.G-.S. 



