Vol. 54.] AND THE COEALLINE CRAG. 339 



sand, about 6 inches thick, and 3 or 4 yards long, which is exposed 

 in the side of a gangway leading down into a deep Crag pit, used 

 as a bullock-yard. In it occur, in the order of their abundance, 

 Gyprina islandica, Cardita senilis, Cardium decorticatum, Mytilus 

 edulis, Venus casina, and some other of the larger characteristic 

 Crag species, with a few smaller ones, such as Limopsis aurita, 

 Cyiherea rudis, Venus ovata, and Mactra triangvla. They are quite 

 perfect, and in similar condition to those that may be found in the 

 shelly sands at Gedgrave or Sudbourne. The matrix in which they 

 are embedded resembles that of the shelly sands of those localities, 

 being composed of calcareous matter full of minute shell- fragments, 

 and containing much glauconite. It has been to some extent 

 coloured by infiltration from the overlying ferruginous beds, but 

 the fragments of the arragonite-shells and the grains of glauconite 

 have not been afi'ected thereby to any great extent. The same seam 

 is seen in the pit itself (see fig. 10, p. 341) to occur in the midst of 

 the ferruginous rock-bed, but it appears to be gradually losing its 

 unaltered coudition,^ the small shells and the shell-fragments having 

 disappeared, and only the thick and strong specimens, such as 

 Gyprina, remaining. Tracing the seam laterally along the sides of 

 the pit, the Gyprinm are replaced by casts, with an occasional valve, 

 almost decomposed, and in a very friable condition.^ 



In another pit at Iken (No. 28), below the last and near the 

 marsh, there is a similar seam of large shells, in the ferruginous 

 rock, but in the form of casts only. These Gyprina-hediB, which 

 have been supposed to be distinctive of Prestwich's zone D, and 

 which I have traced to the base of the Crag, are thus found to 

 exist also in what is evidently the highest part of the formation. 



Beds containing the casts of large shells are found in all the 

 Aldeburgh sections, as at Nos. 29, 31, 32, & 33.' At pit No. 31, 

 near the railway -station, the seam is from 4 to 6 feet thick, and 

 contains, in addition to the species found at Iken, specimens of 

 Valuta Lamherti (very large) and Panopcea Faujasii.^ Beds of 

 large shells in the form of casts are quite as abundant in the upper 

 part of the Crag at Iken and Aldeburgh (Prestwich's zone G) as the 

 shells themselves are in the lower portion (zone D) at Sutton, Ged- 

 grave, and Sudbourne.^ 



^ The sharp fracture, when they are broken, of the shells in the gangway 

 (fig. 9) is in striking contrast with the soft and marly condition of some of 

 the specimens in the pit-section (fig. 10). 



"^ Mr. Kendall informs me that some years ago, by digging through the floor 

 of the pit of indurated Crag at Aldeburgh (No. 32), he found a number of 

 specimens of Cardium decorticatum in a similarly rotten and partly decalcified 

 condition. 



^ At pit No. 34 there is a seam containing specimens of Mytilus in great 

 profusion, a form which is by no means so abundant at other localities. 



* I bored here for 20 feet, through comminuted ferruginous Crag, without 

 reaching the shelly sands. 



^ It has been shown that large species of moUusca occur abundantly in 

 places in the upper or ferruginous part of the Crag. It can hardly be 

 supposed that small forms were absent from the sea of that period, but in 

 material so loose and friable it is less probable that traces of them would be 

 preserved. 



