LATER TERTIARY GEOLOGY OP EAST ANGELA. 119 



comparison with what it possesses where it takes its place north- 

 wards, and rests directly on the older formations *. 



It is in this way that we trace the relation and succession of the 

 beds of the Glacial formation which are posterior to the Contorted 

 Drift, the clay of the North of England being posterior to that of 

 East Anglia, and the mountain-drift and high-level sands of Wales 

 and Lancashire posterior to both, having been formed when the ice 

 which, during the earlier stages, had kept the sea out of the deeply 

 depressed land, had so retreated and shrunk as to leave the north of 

 Britain a snow-capped archipelago. A comparison of the molluscan 

 remains of the Middle Glacial, of the Upper as revealed by shell- 

 bearing sand bands occurring in it at Dimlington and Bridlington, 

 and of these high-level sands is in the strictest accordance with this 

 succession. The details of the mollusca of the Upper and Middle 

 Glacial will be found in the tabular lists of the Supplement to the 

 ' Crag Mollusca,' with slight additions in the note at the end of this 

 paper, while those of the high-level sands are to be found in that given 

 by Mr. Darbishire f ; and it will be seen that while several Crag spe- 

 cies, now either unknown as living or known only as living in remote 

 and mostly more southern seas, occur in the Middle Glacial, only 

 one or two such have been found in the Upper, and these in associa- 

 tion with many very arctic species ; while in Mr. Darbishire's list 

 of these high-level sands none but species still living occur, and 

 these all, with the exception of two or three arctic forms, still sur- 

 viving in British seas. 



Note, % Mr. S. V. Wood, F.G.S., the Author of the ' Crag Mollusca,' 

 on new Occurrences of Species of Mollusca from the Upper 

 Tertiaries of the East of England. 



Red and Coralline Crags. 

 Nassa conglobata, Brocchi. (Crag Moll. p. 32, v. Suppl. p. 15.) 



The only specimen of this species known to me at the time of the 

 publication of the Supplement to the ' Crag Mollusca ' consisted of a 

 solitary but perfect one found by Mr. Charlesworth, many years ago, 

 at Walton Naze. Mr. Canham, however, has since found a specimen 

 in the Red Crag of Sutton, in contiguity to the outlier of Coralline 

 Crag ; and I am now inclined to think that, like such shells as Tro- 

 phon elegans and Cassidaria bicatenata, formerly supposed to be 

 Bed and not Coralline Crag shells, Nassa conglobata is really a Coral- 

 line-Crag species, and occurs in the Red Crag only by derivation. 

 It may, perhaps, be objected that this is an unwarranted conclusion, 



* In wells and in railway-cuttings and sinkings beneath them in Cambridge- 

 shire and Huntingdonshire the Upper Glacial has been found to possess a thick- 

 ness exceeding 150 feet. We are not aware of its having been found to have 

 more than a third of this thickness where underlain by the Middle Glacial. 



+ Geol. Mag. vol. ii. p. 298, and Quart, Journ. Geol. Soc. vol. xxx. p. 40. 



