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 A HISTORY OF NORFOLK The occurrence of shells in the Crag is very local, in many sections we find no fossils ; but it is natural that only the fossiliferous localities have attracted great attention.' In some places Nucula cobboldia, in others Cyprina islandica, or Scrobicularia plana abound. Almost every- where Tellina obliqua^ T. pratenuis, Pecten, Cardium, Mactra, Cerithium tricinctum and fish-remains occur where shell-patches have been opened up. The lower beds more usually contain shells because of the protec- tion afforded by bands of clay, which, where prominent, are usually re- garded as Chillesford Clay. Above this horizon we sometimes find layers of iron-pan or ferruginous sandstone and gravel with casts of shells. Ochreous nodules also occur, and these appear to be due to the contem- poraneous breaking up of clay-seams, the clay pebbles thus formed having acted as nuclei for the subsequent deposition of brown iron ore. Ochre was formerly obtained from the Crag Series at Eaton, near Norwich. To the occurrence of two bands of shells at Bramerton Mr. J. E. Taylor drew attention in 1865. The higher band has been recognized as containing a larger percentage of northern moUusca, and its more abundant species belong to somewhat deeper water, while in it there are fewer land and freshwater moUusca than in the lower band. Three horizons of shells occur locally at Whitlingham, while at Thorpe, the highest stage, which yields casts of shells, is newer than any of the shell- beds at Bramerton and Whitlingham. This highest stage at Thorpe is approximately equivalent to the Weybourne Crag, which overlapping other stages occurs directly on the Chalk at Weybourne. It is also met with in places in the Bure valley, as at Belaugh (hence the name Bure Valley Crag). All the marine shells found in this newer Crag, except 'Tellina balthica, and Anomia striata occur also in the lower portions of the Norwich Crag, but the assemblage of species is more arctic in character. On account of the presence, and indeed abundance, of the Tellina^ this highest sub-division has also been termed the Tellina-balthica Crag. Towards the upper part of the Norwich Crag there is locally developed, as at Aldeby, Surlingham, Wroxham and Coltishall, masses or 'jambs ' of micaceous sandy clay, or clay interlaminated with films of sand, and known as the Chillesford Clay, from the village of Chillesford, near Orford, in Suffolk. This clay, which is from i to 18 feet thick, has been used for brick-making at the localities above-named, and also at Eaton near Norwich, where a pottery kiln existed in the time of Queen Anne. The Crag yields water, especially when the Chalk is water-logged, and the higher portions of the series yield water, which is locally upheld by the Chillesford Clay. Above the horizon of the Weybourne Crag occurs the famous Forest Bed Series, or Cromer Forest Bed, an accumulation which immediately preceded the Glacial deposits. Evidence of increasing cold is furnished in the deposits overlying this series. Huge bones of elephant and rhinoceros have been known since early times to occur in the Forest Bed, and they gave rise to the tradition M
 * See S. V. Wood, Monograph of the Crag MoUusca (Palseontograph. Soc).