Vol. 56.] MR. F. W. HA.RMER ON THE CR1G OF ESSEX. 709 



the Newer from the Older Pliocene between the Lenham Beds (con- 

 taining Area diluvii. 1 and other characteristic Italian Pliocene or 

 Miocene shells of the North Sea basin) and the Coralline Crag, 

 regarding the latter as the oldest member of a more or less con- 

 tinuous and closely connected series of Newer Pliocene age. 



The Gedgravian Beds seem to be approximately equivalent to the 

 Belgian zone a Isocardia cor, as suggested by M. Van den Broeck. 

 The Lenham and Folkestone Beds, on the other hand, not only closely 

 resemble the sands of Diest and Louvain lithologically, but are con- 

 nected stratigraphically with them by a more or less continuous 

 chain of outliers always occupying high ground, as pointed out by 

 that observer. He formerly separated the Antwerp Beds a Isocardia 

 cor from the Diestian Sands under the term Casterlien 2 (originally 

 proposed by Dumont), and I suggest that it might be desirable to 

 revive that classification. If, as I think, the Lenham deposits are 

 distinct from the Coralline Crag, the zone a Isocardia cor may be 

 equally distinct from the ferruginous sandstones of Belgium. 



II. The Crag of Essex — Waltonian. (See Map on p. 710.) 



The Red Crag beds for which I propose the term Waltonian 

 are confined to the county of Essex, and are distinguished, as is the 

 Walton deposit, by the strongly marked southern facies of their 

 molluscan fauna, and especially by the abundance of the southern 

 species, Neptunea contraria, and the absence, except in the Oakley 

 sub-zone as explained farther on, of the dextral form, Neptunea 

 antiqua, 3 and its northern allies N. despecta and N. carinata. The 

 study of the comparative abundance of these two groups at different 

 horizons in the Crag is of considerable importance. The sinistral 

 species, so characteristic of the Essex Crag, becomes less abundant 

 at the various exposures in Suffolk as we trace them northward, 

 and it is rarely met with in Norfolk. The dextral shell, on the 

 contrary, almost unknown at the Walton horizon, is increasingly 



1 I am not aware that any species, which is as specially characteristic of the 

 Coralline Crag as Area diluvii is of the Lenham Beds, can be pointed out as 

 absent from Walton. 



2 ' Diestien, Casterlien & Scaldisien,' Ann. Soc. Roy. Malac. Belg. vol. xvii 

 (1882) Bull. pp. ciii-cviii. 



3 I have given elsewhere, Proc. Internat. Congr. Zool. Cambridge (1898) 

 p. 222, my reasons for believing that Neptunea antiqua and N. contraria are not 

 varieties of the dextral form as now generally supposed, but, as originally 

 described by Linngeus, distinct species. These migrated separately into the Crag 

 area from the north, N. contraria arriving at an earlier period, and penetrating 

 during the Pliocene epoch farther southward than N. antiqua. At present, 

 moreover, the sinistral shell is not known living farther north than Vigo Bay, 

 on the western coast of Spain ; while the dextral N. antiqua, and especially its 

 carinated representatives, have a northern range. The reversed specimens of 

 N. antiqua occasionally met with in British seas are doubtless monstrous varieties 

 of the dextral shells with which they occur, and which they closely resemble. 

 The sinistral shells of the Crag, on the contrary, are allied to the species now 

 living in Vigo Bay, and to N. sinistrorsa, of the Sicilian Pliocene. No reversed 

 (that is, dextral) specimens of the Crag form N. contraria have ever 

 been met with. 



