INTRODUCTION. 



501 



those of the Norjvich zone, connecting it with the latter as well as with the 

 Ardennes, probably representing one of the channels by which the drainage of 

 that region then reached the sea. The abrupt disappearance towards the north of 

 typical Chillesford beds near Burgh may have been due, I suggest, to the invasion 

 of this region by the Weybournian sea. If my view of the case is correct, it follows 

 that a slight elevation of this region took place at this stage, the shallow sea of the 

 Norwich Crag being for a time converted into land traversed by the micaceous and 

 sheltered waters of the Chillesford estuary. 



Fm. 5 —Map showing the principal exposures of undoubted Chillesford Clay (marked +) between Chillesford 

 in Suffolk and Burgh in Norfolk in the Bure valley, the probalile course of one of the estuaries of the Rhine 

 during this stage. The dotted area is that covered by the Westleton shingle of Prestwich (Pleistocene). 

 — F. W. H. (Reproduced by permission of the C'oimcil of the Geologists' Association.) 



The total number of the more characteristic mollusca of the horizon represented 

 by the Chillesford Church-pit is not great, but they differ considerably from those 

 of the Norwich and Weybourne zones, conditions suggesting a difference in the con- 

 ditions under which they were deposited. Among them may be specially mentioned : 

 Turritella communis. ■ Leda ohlongoldes. 



Nucida tenuis. Gardium (Serripes) groenlandicum. 



Leda lanceolata. TeUina {Macoma) calcarea. 



66 



