The cause of this singular discrepancy has been dealt with elsewhere; it probably 

 arose in the main through the exceptional physiography of the North Sea basin in 

 Middle and Newer Pliocene times. Throughout these periods the North Sea formed a 

 basin open to the north only, so that only cold currents could enter, and only pelagic 

 larvae from the north could drift in, to replace such southern forms as were locally 

 exterminated by exceptional winters. Thus without much real change of average temper* 

 ature the marine fauna became more and more arctic as time passed. Britain, on the 

 other hand, was attached to the continent of Europe on the south only, and had no 

 land*connexion northward. Its eastern part was also traversed by rivers rising many 

 degrees to the south, in Central France and the Alps. Britain therefore could only 

 receive southern land and freshwater species, and the discordance between the marine 

 and the freshwater species, as indicators of climate, would become more and more 

 marked as long as the Strait of Dover still remained closed. 



Thus it happens that we now find, mingled in the same Upper Pliocene estuarine 

 deposits in Britain, a southern land*fauna and a subarctic marine fauna, whereas the 

 climate, as shown by the plants, was little different from that now existing. Plants, which 

 give the best indications of the real climatic conditions, unfortunately have not yet been 

 found in any of the British Pliocene deposits older than the Cromerian stage. 



It will be understood from the foregoing remarks that there still remains much 

 uncertainty as to the exact correlation of the strata ; but we may tentatively place the 

 two plant*bearing deposits now to be described in approximately the positions shown 

 in the subjoined table: — 



PLIOCENE DEPOSITS OF THE NORTH SEA BASIN. 



Pleistocene 

 (base) 



Upper 

 Pliocene 



Middle 

 Pliocene 



Lower 

 Pliocene 



ENGLAND. NETHERLANDS AND BELGIUM. 



Glacial and Interglacial beds Diluvium 



Arctic Plankbed 

 Leda*myalis bed 



Cromerian 

 Weybourn Crag 

 Chillesford Crag 

 Norwich Crag 



Red Crag of Butley 



? 



Walton Crag 

 (unconformity) 

 i Coralline Crag and 

 I Lenham Beds 



? 

 ? 



not yet recognised 



Teglian 

 Amstelian 

 Reuverian 

 Scaldisian 



Diestian 



"Boxsstones" with derivative 

 Early Pliocene or Miocene fossils 



Miocene 



