Vol. 56.] MR. F. W. HARMER ON THE CRAG OF ESSEX. 727 



nodule-bed at Waldringfield and elsewhere, at some distance 

 from any known exposure of the older deposit. Shells from, the 

 Coralline Crag are not coated with silicate, as are those from 

 older Tertiary formations, and being composed, as a rule, of pure 

 carbonate of lime, are more or less fragile, so that some of them 

 can only be extracted in perfect condition with the most elaborate 

 care and great difficulty. It is not easy to understand that such 

 fossils could have survived the rough treatment to which, on the 

 derivative hypothesis, they must have been exposed in the shallow 

 Eed Crag sea, whose waves reduced a great part of the shells of 

 molluscs then living in it to a mass of indistinguishable fragments. 1 

 Many of the species formerly looked upon as derivative from the 

 Coralline Crag have been obtained in recent years from the Scal- 

 disian of Belgium, 2 and the still later Amstelian deposits of Holland ; 

 and, moreover, we find that in the Norwich Crag, where the idea of 

 derivation is not suggested, some characteristic Coralline Crag forms 

 occur occasionally, in certain localities only. 



In the Third Supplement to the Monograph of the Crag Mollusca, 

 published in 1882 (after his father's death), S. V. Wood, Jun, main- 

 tained, when dealing with the Crag of Felixstowe (JSTewbournian), that 

 a considerable number of the species found at that place, including 

 such forms as Oyprcea avellana, Voluta Lamberti, Nassa reticosa, 

 Purpura tetragona, Trophon costifer, Pectunculus subobliquus, and 

 Artemis lentiformis, had been derived from the destruction of earlier 

 Eed Crag beds (Waltonian) formerly occupying the Newbournian 

 area. 3 I am compelled now to differ from my old friend, though 

 with great regret. The Eed Crag deposits, I believe, were strictly 

 littoral, and as the sea was gradually retiring northward, it was 

 rather leaving behind it beds which it had accumulated at an earlier 

 stage, than eroding them. 4 If the shells mentioned above had ceased 

 to exist during the later part of the Eed Crag Period, they ought 

 to have been deposited at the base only of the different exposures of 

 the more recent zones : that is, when the sea was {ex hypothesi), 

 as it began to occupy a new area, destroying and reconstructing 

 any earlier shell-banks that may have existed there ; but this is 

 not the case, so far as I know. 



The species just named, supposed by Wood to be Waltonian only, 

 occur, moreover, in every part of the Eed Crag, and at localities like 

 Butley, the fauna of which has not been generally thought to 

 contain derivative shells. 5 



1 The rolled and worn condition of some of the specimens supposed to have 

 been derived from the Coralline Crag appears to me an argument against, rather 

 than for, their extraneous origin. 



2 41 out of the 104 species regarded by Wood as derivative, and 27 out of the 

 46 given by Presfrwich as such, occur in the Belgian or Dutch beds. Of the 

 rest, I have found about 30 at Little Oakley or Beaumont. 



3 S. V. Wood, Jun. and I had suggested a similar view in 1872, ' 1st Suppl. 

 Crag Moll.' Monogr. Pal. Soc. p. vii. 



4 It must be admitted, however, that the Eed Crag south of the Stour has 

 been much denuded. 



5 It is, of course, possible that, in the constant rearrangement by the waves 

 of the shelly material composing the beaches of the Red Crag sea, some 

 specimens may have found their way from the Waltonian to the Newbourniau, 



