238 Geological Society of London, 



plain ; and out of this again the valleys of the existing streams have 

 been scooped, 



The gravels of the upper plain are a marine deposit, and indicate 

 a marine denudation of great antiquity, followed by an emergence, 

 during which the old valleys were scooped out of that plain. The 

 gravels of these valley-plains were formed during a subsequent sub- 

 mergence ; they contain bands of clay and loam passing into Boulder- 

 clay, and are probably marine. This submergence continued until 

 the Boulder-clay was deposited on the top of the higher-plain 

 gravels ; and then succeeded a period of emergence, during which the 

 present valleys were scooped out of the lower plain. 



II. March 11th, 1868.— "On the Structure of the Crag-beds of 

 Norfolk and Suffolk, with some observations on their Organic 

 remains. — Part I. Coralline Crag." By Joseph Prestwich, Esq., 

 F.E.S., F.G.S., etc. 



The history of the division of the several Crag-deposits into three 

 formations — the Mammaliferous, Red, and Coralline Crags — having 

 been recounted, the author stated that for the last thirty years the 

 evidence of their sequence had remained unaltered, the distinction 

 between the Mammaliferous and Red Crags being still purely 

 palseontological, not a single case of superposition having been dis- 

 covered. Mr. Prestwich then proceeded to the special object of 

 this paper, which was to describe more fully the physical structure 

 of the several crags, and to determine, if possible, the exact relation 

 which the Suffolk Crags bear to the Crag of Norfolk. 



Commencing with the Coralline Crag, the author stated that the 

 well-known outlier at Sutton furnishes a base-line and the best clue 

 to its structure and dimensions, showing also the depth to which it 

 has been denuded and replaced by the Red Crag. The Coralline 

 Crag is generally described as consisting of two divisions : — an upper 

 one, formed chiefly of the remains of Bryozoa, and a lower one of 

 light-coloured sands, with a profusion of shells ; and the author 

 now gave their exact dimensions and his proposed subdivisions, as 

 follows : — 



Character and Thickness. Localities. 



>^ 



U 



'^^ \h. Sand and comminuted shells, 6 ft. Sudbourne and Gedgrave. 



^ '^^ { y- Comminuted shells and remains of Bryozoa, Sutton, Sudbourne, Ged- 

 g g f forming a soft Building-stone, 30 ft. grave, Iken, Aldboro'. 



f/. Comminuted shells, with numerous entire Sutton, Iken, Orford, High 



small shells, 5 ft. Gedgrave. 



Sands with numerous Bryozoa, and some Sutton, Broom Hill. 



small shells and Echini, 12 ft. 



Comminuted shells, large, entire, and double Sutton, Broom Hill, Sud- 



^ shells, and bands of limestone, 15 ft. bourne. 



e. Marly beds, with numerous well-preserved Sutton, Ramsholt. 



and double shells, 10 ft. 



b. Comminuted shells and Cetacean remains, 4 ft. Sutton. 



a. Phosphatic nodules and mammalian remains, Sutton. 

 1 ft. 



