GEOLOGY are of Mediterranean type. The formation as noted by Mr. Harmer was laid down in water of moderate depth as submarine shell-banks with drifted mollusca and with occasional reefs of bryozoa, RED CRAG The Red Crag is a reddish and yellowish brown sand with much oblique and false bedding, with abundant mollusca, some broken and most of them stained red. Rusty brown veins of ironstone and films of ferruginous sandstone pervade the strata. The iron ore, as suggested by J. E. Taylor, may have been derived to some extent from pyrites in the London Clay, but much of it, according to Prestwich, appears to have been introduced subsequently, as the staining and the infiltration bands are very irregularly distributed. The Red Crag has been opened in places to a depth of 1 5 or 20 feet, while its full thickness does not appear to exceed 40 feet, if we accept Mr. Harmer's grouping, and regard as Norwich Crag those beds which lie to the north of Aldeburgh. The Red Crag rests irregularly on the worn surfaces of the Coral- line Crag and elsewhere on the London Clay. Lyell described an old cliff in the Coralline Crag at Sutton against which the Red Crag rested,' and the two crags have been seen in irregular conjunction at Tattingstone Park and Ramsholt. In opposition to earlier observers Mr. Harmer believes that not many of the Red Crag mollusca have been derived from the Coralline Crag, although he admits that upheaval and some denuda- tion of the older deposit took place, and that its basement bed remained in certain areas to form the foundation of the Red Crag.^ It is generally agreed that the older portion of the Red Crag is that of Walton-on-the-Naze, a stage not recognized in Suffolk. In that region it contains most of the characteristic Coralline Crag shells, as well as mollusca which entered the crag basin from areas on the north with which communication had been opened up. Thus Mr. Harmer has come to regard the Red Crag as the marginal accumulations of a sea which gradually retreated northward, so that the deposits as we approach Norfolk yield species more boreal as well as more recent in character. The oldest layers of Red Crag in Suffolk would be those that occur between the Stour and the Orwell, at Shotley and Erwarton, at Tatting- stone and Bentley, and as far west as Stoke and Polstead in the neighbour- hood of Sudbury. These beds have not been separately designated by Mr. Harmer, who groups the Suffolk Red Crag into two stages, based on the abundant forms that occur in the districts. The older he terms the Newbournian, from Newbourn, south of Woodbridge ; it constitutes the zone of Mactra constricta, and includes the well-known Red Crag of Felixstow, which rests on the London Clay in the cliff section, and also the Crag at Trimley, Ramsholt, Sutton and Shottisham. • Proc. Geol. Soc. iii. 127 ; Prestwich, ^art. Jount. Geol. Soc. xxvii. 339, 342.
- ^art. Journ. Geol. Soc. Ivi. 707, 708, 719, 721 ; Proc. Geol. Assoc, xvli. 428.
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