PROCEEDINGS
OF
THE GEOLOGICAL SOCIETY.
POSTPONED PAPER.
On the Structure of the Crag-beds of Suffolk and Norfolk, with some Observations on their Organic Remains. By Joseph Prestwich, F.R.S., F.G.S., &c. Part II.— The Red 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 † , whose list leaves little to be added, except the more special determination of their local distribution. To Mr. Searles Wood, jun.‡, 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 || . To the palaeontographical 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 siliceous 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.
† Paleont. Soc. Trans. 1848-56.
‡ Ann. & Mag. Nat. Hist. March 1864.
§ Quart. Journ. Geol. Soc. vol. xxii. p. 19.
|| Ibid. p. 538.
VOL. XXVII. PART I. 2 A
