350 MR. r. W. HAEMER ON THE LENHAM BEDS [Aug. 1 898, 



seems also to indicate that the Coralline Crag is not so much a 

 fragment of a once widely-spread formation as has been often 

 supposed, but one of a series of banks, which existed in a part of 

 the sea where, owing to the bottom being continuously swept by 

 strong currents, no general deposition of sediment was taking 

 place. 



The presence of currents causing the accumulation of banks of 

 shelly sand in sheltered spots does not seem so favourable to the 

 growth of moUusca, which flourish most in less exposed situations. 

 Along the convex portion of the Norfolk coast at the present day 

 between Weybourne and Yarmouth, molluscs are but rarely met 

 with ; but on the more sheltered part, from Wells to Hunstanton, 

 where the influence of the tidal currents coming from the Lincoln- 

 shire coast is less felt, shells lie in places on the beach as thickly 

 as they do in the Crag-beds. 



Polyzoa, on the contrary, seem to flourish best in clear water 

 agitated by currents, and their great abundance in the Coralline 

 Crag, not only in the form of comminuted material, but in places 

 in their original position of growth, is especially worthy of notice. 

 D'Orbigny's remarks on the habits of polyzoa, made in 1850, seem 

 to me so applicable to our present enquiry that I venture to quote 

 them in full. He says, ' Qu'ils vivaient dans des eaux agitees, ce 

 qui est prouve par le manque de sediments vaseux et surtout 

 par les lits inclines des couches, comme on le reconnait si bien sur 

 tous les points, lits inclines speciaux aux bancs sous-marins formes 

 par Taction des courants dans les mors anciennes comme dans les 

 mers actuelles.' ^ 



The connexion of the Coralline Crag sea with the Atlantic by 

 means of a channel or strait over some part of the South of England 

 seems to be indicated not only by the close correspondence of the 

 moUusca of that formation with those of the Mediterranean,^ but 

 also because in a closed basin no such currents as those to which 

 I think the deposition of the Coralline Crag was due could have 

 existed. 



As we have seen, the currents which attend the flowing tide along 

 the English shores of the North Sea come from the north, and not 

 through the Straits of Dover. The fact of the great subsidence, 

 regularly increasing in a northerly direction, which has affected 

 Holland, and possibly Scandinavia,^ since the Diestien period is an 

 additional reason for thinking that the Coralline Crag sea may have 

 been less open to the north than it is at present ; and if this was 

 so, the velocity of the tidal currents flowing through the southern 



^ 'Paleont. Eran9. — Terr. Cretac. (Bryozoaires) ' vol. v, p. 11; see also 

 Prestwich, Quart. Journ. Geol. See. vol. xxvii. (1871) p. 129. 



^ The correspondence between the existing molluscan fauna of the Mediter- 

 ranean and that of the Coralline Crag has been often emphasized, but there is 

 also much resemblance between the latter and that of the older Pliocene beds 

 of Italy and Sicily. Many species, of course, occur in the last-named which 

 did not live at that period in our northern latitudes. 



^ There seems to be good reason for supposing that Scandinavia formerly 

 stood considerably higher than it does at present. 



