PROCEEDINGS 



OF 



THE GEOLOGICAL SOCIETY. 



POSTPONED PAPER. 



O/i the Stetjcture of the Crag-beds of Sufpolk and Norfolk, with 

 some OssERVATiojfS on their Organic Eemains. By Joseph 

 Prestwich, F.R.S., F.G.S., &c. Part II.— The Eed Crag of 

 Essex and Suffolk. 



(Read May 20, 1868 * .) 



The superposition of the Red Crag upon the Coralline Crag is clear. 

 The points on which there are some differences of opinion relate 

 chiefly to questions of structure and to the relation of the Crag- 

 beds of Suffolk with those of Norfolk. Like the Testacea of the 

 Coralline Crag, those of the Red Crag have been the object of 

 assiduous research on the part of Mr. Searles Wood f, whose list 

 leaves little to be added, except the more special determination of 

 their local distribution. To Mr. Searles Wood, jun.J, also, we are 

 indebted for an elaborate account of the different stages into which 

 he considers the deposit should be divided, to the Rev. Mr. Fisher 

 for a paper on its relation to the Mammaliferous Crag §, and to 

 Mr. S. V. Wood for a subsequent paper on the structure of the Red 

 Crag 1 1 . To the palseontographical papers I shall have occasion to 

 refer presently. 



The Red Crag of Suffolk covers an area of about 300 square miles. 

 It is, however, so overlain by the sands and clays of the Boulder- 

 clay series, that generally it is only on the sides of the valleys which 

 intersect the district that the Crag-beds come to the surface and 

 are to be seen. The places where they are best exposed are on the 

 slopes of the hills skirting the rivers Orwell and Deben, and in the 

 cliff-sections at Bawdsey and Felix stow. As before mentioned, the 

 Red Crag occupies an excavated area in the Coralline Crag, wrapping 

 round the isolated reefs of the latter, filling up the hollows between 

 them, and lying nearly on a level with the conterminous Coralline 

 Crag. Whilst the Coralline Crag consists essentially of light-coloured 

 calcareous beds with an admixture of sUiceous sand, the Red Crag 

 consists of a base of siliceous sands with more or less of the peroxide 

 of iron and a few thin seams of clay. They form such an extremely 

 variable series that I have failed to observe any definite order of 

 succession in the various beds of the lower series, or to recognize 

 the " Beach-stages " of Mr. S. Wood, jun. I would divide them into 

 two groups only — the lower one characterized by the prevalence of 



* For the discussion on this paper see Quart. Journ. Geol. Soc. vol. xxiv. 

 p. 462. 



t Palffiout. Soc. Trans. 1848-56. J Ann. & Mag. Nat. Hist. March 1864. 



§ Quart. Journ. Geol. Soc. vol. xxii. p. 19. || Ibid. p. 538. 



VOL. XXVII. PART I. 2 A 



