PlIOCENE PEEIOD IN ENGLAND. 517 



of any essential character beyond the fluvio-marine admixture in 

 the latter ; and this negatives any explanation of the difficulty by 

 supposing that the species in question were peculiar to the eastern 

 side of England. 



It will, I trust, appear clear from the preceding pages of this 

 paper that the general submergence preceded the formation of the 

 Chalky Clay ; and had I space I could offer many reasons to show 

 that it preceded both the Purple Clay of Yorkshire and the Lower 

 Boulder-clay of the north-west containing shells ; and I think it must, 

 from what I have shown, be obvious to geologists that the Base- 

 ment Clay of Holderness was formed when the inclination of England 

 was in accordance with that which prevailed at the commencement 

 of Stage II., and when the extinct Mollusca which are found in it 

 still survived from the time of the Crag in the continuation of the 

 sea of which, while still confined to the eastern side of England, the 

 Bridlington and Dimlington shells lived. Had the Purple Clay and 

 the Lower Clay of the north-west been followed by the submergence, 

 the gravels which then accumulated up to 1200 feet in Lancashire, 

 and 1350 in North Wales, would everywhere rest upon it ; but in 

 the case of the Purple Clay there is no marine gravel at aU over it, 

 save the Hessle, which is at very low elevations ; and in the case of 

 the clay of Lancashire, none, so far as I can learn, at levels above 

 that of Macclesfield Cemetery, which is given by Mr. Darbishire as 

 600 feet, and is less than that to which the gravel e should, by the 

 westerly increment of submergence beyond the place of fig. XYIL, 

 rise. As regards moraine accumulated in the north-west during 

 the sinking of the land in Stage II. I will speak further on. 



As from the altering inclination of the land and increasing sub- 

 mergence in the westerly direction, the ice, of which the Basement 

 Clay of Holderness was the moraine, and which had furnished mo- 

 rainic material to the sand hi, and so gave origin to the Till of 

 Cromer {h 2\ retreated through the Humber, the Basement Clay 

 became covered by the sea to a considerable depth, during which 

 the Bridlington bed was laid down upon it. The seam at Dimlington 

 was probably buried by a temporary advance of the ice and of its 

 moraine during this retreat, and molluscan remains of the same 

 period were preserved in the bed of the sea, which had now ex- 

 tended over Western Norfolk ; and as the ice began, with the rise of 

 the land, to advance in a difi'erent direction, in accordance with the 

 changed inclination, it ploughed off such of these deposits, corre- 

 sponding in age with the Dimlington and Bridlington beds, as lay 

 in its path, and their debris, carried away by currents, was imbedded 

 again in the gravel c in the way described in Stage III. ; and thus 

 it is that we get in the seam x in fig. XIII. , the peculiar sheU of 

 Bridlington, Venus fiuctuosa, and those other shells of that place 

 which, before the culmination of submergence, had become extinct, 

 such as Nucula Gohholdice and Tellina ohliqua. These, together with 

 several other Crag species found in the seam ^, though they had 

 disappeared from British seas when the submergence culminated, 

 were yet living there in the earlier portion of that very long interval 



