Vol. 56.] MR. F. W. HARMER ON THE CR1G OF ESSEX. 721 



regarded as belonging to a period distinctly later than the rest of 

 the Red Crag. 



Neptunea antiqua (dextral) is at Butley nearly as abundant as 

 JV. contraria. Several species of Leda are there met with not unfre- 

 quently, an.&J\ r iicula Cobboldice is very common ; while Tellina obliqua, 

 T. prcetenuis, Mactra ovalis, M. constricta, and Cardium angustatum, 

 with some recent British species, are so abundant as to make up a 

 large proportion of the total number of specimens present. The 

 following northern shells may be noted as more abundant in the 

 Butley zone than in beds of an earlier age, namely : Trophon altus, 

 Buccinum groenlandicum, Natica groenlandiea. and Cardium groen- 

 landicum. At the same time the proportion of extinct and southern 

 shells is considerably smaller at Butley than in the Newbournian 

 Crag. 



There are other exposures of Crag at Alderton, Hollesley, and 

 Bawdsey, containing a fauna similar to that of Butley, the arctic 

 shell, Cardium groenlandicmn, very rare in the Newbournian deposits, 

 being especially characteristic of the last-named locality ; and for 

 these, with the Crag of Sudbourn and Iken, and of the stack-yard pit 

 at Chillesford, 1 1 propose the name Butley an. This division has a 

 more recent as well as a more boreal fauna than that of the horizons 

 before mentioned. 



The distinction between the Butleyan and the Newbournian zones 

 seems to me to be more marked than that between any of the other 

 divisions of the Red Crag (see analysis of molluscan fauna, p. 725). 



For the deposits hitherto known as Norwich Crag (an horizon 

 of greater thickness and importance than was formerly supposed), 

 which extend more or less continuously from Aldeburgh in Suffolk to 

 Horstead and Burgh in Norfolk, a distance of more than 40 miles in 

 one direction, and 20 miles, from Hoxne to Southwold, in another, I 

 adopt the name Icen i an, originally proposed for the Crag-formation 

 generally by S. P. Woodward. 2 These beds, in places nearly 200 feet 

 thick, occupy an entirely different area from that of the lied Crag, 

 and contain' a fauna which differs- more widely from that of the 

 latter, than the various divisions now proposed for it do one from 

 the other. 



A number of the characteristic shells, extinct and southern, of the 

 older Crag had lingered on in the North Sea, though in gradually 

 diminishing numbers, until the Butleyan Period, of which the 

 following may be mentioned (but they apparently became extinct in 

 the Crag basin before the Icenian Period, killed off possibly by the 

 rapidly increasing cold) : — 



1 I am now disposed to think, for the reasons given on p. 734, that the 

 highest bed at this pit, containing Scrobicularia piperata, formerly regarded by 

 S. V. Wood, Jun. and myself as representing the Norwich zone, belongs to the 

 newest part of the Butleyan division. 



2 Norwich is supposed to stand on the site of the ancient Venta Icenorum. 



Q. J. G. S. No. 224. 3 c 



