Vol. 56.] MB. F. W. HAEMER ON THE CRAG OF ESSEX. 731 



The Red Crag deposits rest against, rather than npon, the 

 Coralline Crag. At Sutton, the well-known case of a bed of My till 

 in place, with adherent valves, indicates, in Prestwich's opinion, an 

 old shore-line. 1 Both the small outlier of Coralline Crag at Sutton, 

 to which near tide-marks this colony of mollusca attached them- 

 selves, and the larger one extending from Gedgrave to Aldeburgh, 

 which does not appear to have been submerged by the Eed Crag 

 sea, must have formed, at that time, islands in it. We have 

 therefore a datum-line, more than 12 miles long from south-west 

 to north-east, by which we may fix, with some approach to accuracy, 

 the depth of the shallow water in which the Red Crag originated. 2 

 Messrs. A. & R. Bell, however, have expressed the opinion that the 

 Red Crag fauna is at some localities, as at Waldringfield, of a deeper- 

 water character than it is at others. 3 If this were so, it would 

 indicate a difference, not in the former depth of the sea at such 

 spots, but in the direction of the currents, or the strength of the 

 wave-action which prevailed there. 4 No instances occur in the Red 

 Crag of an undisturbed sea-bottom, except the unstratifled bed at 

 the base of the section at Walton Cliff, and one or two similar cases 

 on a smaller scale. The fossils of the Red Crag are, with these 

 few exceptions, the drifted and stratified shells of dead mollusca, 

 deposited either against the shore, or in shallow water in proximity 

 to it. 



At the present day, it is in land-locked or sheltered bays, or 

 within the embouchures of estuaries, that, on the English coast, 

 sandy sediment is mostly accumulating. Along those parts that 

 are exposed to the action of tidal currents, the beach travels, but on 

 the whole it does not increase in extent seaward ; sheltered bays, 

 however, act as catchment-areas, arresting its progress, and it is 

 under such circumstances heaped np against the shore by wave- 

 action, or it accumulates in shallow water as banks or shoals. 



Where rivers have been discharging in the vicinity, accumulation 

 has naturally gone on to a greater extent, and in proportion to the 

 amount of sediment brought down by them, now, or at some 

 former period : as, for example, on the Lancashire coast in Morecambe 

 Bay, or in the estuaries of the Dee and Ribble ; and on the eastern 

 coast of Great Britain, in the Wash, and the estuary of the 

 Thames, 



Dead shells often accumulate in such sheltered places, as in 

 Morte Bay on the north-western coast of Devon, where the beach 

 is covered with them ; or on Padstow Sands, of which they form 



1 Quart. Jburn. G-eol. Soc. vol. xxvii (1871) p. 340. Mr. P. R Kendall 

 noticed a similar bed of Mytili in the pit at Sudbourn, No. 19 of ray former 

 paper, Quart. Journ. Geol. Soc. vol. liv (1898) fig. 4, p. 32G, where the Eed 

 Crag rests upon the Coralline Crag. 



2 Prestwich observed, moreover, ripple-marks, indicative of a shore from 

 time to time uncovered by the tide, in the Crag at Bawdsey, Quart. Journ. 

 Geol. Soc. vol. xxvii (1871) p. 327 & fig. 7. 



3 Proc. Geol. Assoc, vol. ii (1873) p. 193. 



4 A similar phenomenon may now be observed on our beaches, where the 

 shells of some species are cast up at one spot, and not at another. 



