CHAP. XII.] ICENIAX PERIOD. 243 



Chillesford Beds) ; and it is believed that these Chillesford 

 Beds pass into the upper portion of the Norwich Crag. 

 Generally speaking, the Suffolk type is the more purely 

 marine deposit, and the Norwich Crag a more littoral 

 one. 



The Sutton section described by Mr. Prestwich l is in- 

 teresting as affording definite evidence of subsidence during 

 the formation of the Eed Crag. This crag is here banked 

 up round an island of Coralline Crag, and two distinct 

 shelves or beaches are found, the upper one cutting into 

 the cliff at a height of 9 or 10 feet above the lower 

 one ; each beach has a basal bed of pebbles and phosphatic 

 nodules with large blocks of Coralline Crag derived from 

 the cliff above. A basement bed of this kind, but with- 

 out the blocks of Coralline Crag, is everywhere found at 

 the bottom of the Eed Crag, and yields chalk flints (some 

 very little worn), septaria from the London Clay, (Ter- 

 tiary) sandstones, Cretaceous chert, and fragments of red 

 granite. 



The shelly sands above are from 10 to 30 feet thick, 

 and they have evidently been accumulated in shallow 

 water, the materials being largely derived from the erosion 

 of the older Tertiary deposits and heaped up by currents 

 into shoals and sandbanks, which have been shifted and 

 reconstructed many times before they came to rest in their 

 present position. 



" The Norwich Crag," says Professor Prestwich, " which 

 occupies the contiguous area, and lies on the same level, 

 seems to have been divided from the more open sea of the 

 Bed Crag by a barrier of Coralline Crag, behind which 

 were sandy bays into which flowed a river or rivers, bring- 

 ing down land and freshwater shells, and probably the 

 mammalian remains, from land to the north-west and 



1 " Quart. Journ. Geol. Soc.," vol. xxvii. p. 340. 



