284 Beport.s and Proceedings — Geological Society of London. 



The line separating the Older and Newer Pliocene is now drawn 

 by the author between the Lenham Beds, containing Area dilnvii 

 and other characteristic Miocene species of the North Sea (or of the 

 Italian Pliocene), and the Coralline Crag, the latter being considered 

 as the oldest member of a more or less continuous and closely con- 

 nected series of Newer Pliocene age. The palceontological difference 

 between the Coralline and Walton Crags is shown to be less than 

 has hitherto been supposed. 



The upper Crag deposits arrange themselves in horizontal and 

 not in vertical sequence, assuming always a more boreal and more 

 recent character as they are traced from south to north. They are 

 the littoral accumulations of a sea retreating, not continuously, but 

 at intervals, in a northerly direction. 



A new horizon of the Crag, represented by some beds at Little 

 Oakley, between Walton and Harwich, is described, indicating the 

 period, before the southern mollusca had commenced to disappear, 

 when a few boreal species were beginning to establish themselves in 

 greater or less abundance in the Anglo-Belgian basin. Though 

 hitherto unnoticed, the fauna of this locality has proved to be 

 exceedingly rich, more than 350 species and varieties having been 

 there obtained, from a seam 10 yards long and less than 2 feet in 

 average thickness. 



The three divisions of the Eed Crag now proposed (the exact 

 position of the Bentley bed not having been ascertained at present), 

 namely, Waltonian, Newbournian, and Butlej'an, are distinguished 

 alike by the difference of their faunas and by the position which 

 they occupy. The first, with its southern shells, is confined to the 

 county of Essex ; the second, containing a smaller proportion of 

 southern and extinct, and a larger proportion of northern and recent 

 species, occupies the district between the Orwell and Deben, and 

 a narrow belt of land to the east of the latter river ; the third, in 

 which Arctic forms such as Cardium grcenlandicum are common, 

 is found only farther north and east. All these beds are believed 

 to have originated in shallow and landlocked bays, successively 

 occupied by the Eed Crag sea as it retreated northward, which were 

 silted up, one after the other, with shelly sand. 



The Norwich Crag (Icenian) occupies an area entirely distinct 

 from that of the Red Crag, no instance being known where the one 

 overlies the other in vertical section ; the fauna of the former is, 

 moreover, more boreal and comparatively poor in species. The 

 Arctic species, Astarte borealis, is confined to the northern part of 

 the Icenian area ; its introduction seems to mark a stage in the 

 continued northerly retreat of the sea. The Icenian deposits thicken 

 rapidly northward and eastward, and are believed by the author 

 to constitute part of the great delta-formation of the Rhine. 



The mammalian remains found at the base of the different horizons 

 of the Crag in a remanie bed, containing material derived from various 

 sources, are considered to be also derivative from deposits, older 

 than the Coralline Crag, formerly existing to the south. 



The Chillesfordian (estuarine) andWeybournian (marine) deposits, 



