516 S. V. WOOD, JUN., ON THE NEWER 



Mr. Eome and myself*, and again in a vertical diagram by myself f, 

 as intercalated in the lower part of the Purple Clay, the Basement 

 Clay appearing to us to die out some miles south of Bridlington. 

 It is now, however, said J that the latter extends to Bridlington, 

 and occupies the space there between the beach-line and the chalk 

 floor, a depth of between 30 and 40 feet ; and that this long-known 

 shell-bed rests on its surface and beneath the whole of the Purple 

 Clay, which just there must be in less thickness than at Dimlington. 

 From this it would appear that unless the clay at Bridlington has been 

 planed off, the shell-bed here and the one at Dimlington occupy pre- 

 cisely the same horizon in the newer Pliocene sequence of deposits. 

 Now the Bridlington shells unquestionably lived where they occur, 

 for they are in the most perfect preservation ; and though the sand 

 containing them has, in the specimens I possess, hardened to the 

 condition of rock, the bivalves have both valves adherent and are 

 quite unworn. This fauna, while it presents certainly the most 

 arctic appearance of any known from England and perhaps from any 

 part of Britain, contains the peculiar and now extinct forms Tellina 

 obliqua and Nucida Cohholdice, the first a shell which, appearing 

 rarely in the Coralline Crag, and so rare in the Walton part of the 

 Eed Crag as to be almost unique, becomes more common in this 

 crag between Walton and Butley, while at the latter place, and 

 also in the fluvio-marine crag, the Chillesford bed, and the sands 

 h i, where these are fossiliferous, it swarms. The Nucula is quite 

 unknown in the Walton portion of the Eed Crag, but it is abundant 

 in the Butley and fluvio-marine portions, and occurs in the sands h i. 

 Both species are not only extinct, but the nearest living analogues of 

 the Nucula are confined to the North Pacific Ocean. Besides these 

 there occurs at Bridlington a North-American species {Venus fliio- 

 tuosa) unknown from the Crag, or any other British bed, glacial or 

 otherwise, except that next mentioned. Of these three shells I have 

 found the remains somewhat common in the seam near the top of c 

 (shown by the letter ^ in fig. XIII.); but they are unknown from 

 any other glacial or post-glacial bed in Britain, with the exception of 

 the sand b 1, which yields the two first-mentioned of them. 



Now if the beds of Moel Tryfaen and Macclesfield which contain 

 none of these three species, nor any not still living either in British 

 seas or in those immediately north of Shetland, nor yet a fauna of 

 a character at all so arctic as that of Bridlington, but yet were 

 obviously accumulated when submergence was at its greatest, are 

 older than these of Bridlington and Dimlington, it is a very 

 anomalous circumstance. These three species are equally unknown 

 from the Hessle and Pen gravels of the eastern side of England, 

 which contain no species but such as now live in the sea surrounding 

 the British isles, or in that immediately north of the Shetlands, 

 and yield a molluscan fauna quite as different from that of Brid- 

 lington and Dimlington as that yielded by Moel Tryfaen, between 

 which and the fauna of the Hessle gravel there is no difference 



* Quart. Journ. Geol. Soc. vol. xxiv. p, 149. t Ibid. vol. xxvi. p. 90. 



I Lamplugh, in Geol. Mag. for Nov. 1878, p. 509, and for Sept. 1879, p. 393,' 



