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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