238 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 24, 



was most probably tbe case, the Scaldesien accumulation was of the 

 nature of a dead-shell sand and gravel-bank, like the " cordons litto- 

 raux " of the English Channel and North Sea, and so merely a local 

 condition of sea-bed, the estimate for the thickness of the Crag must 

 be stiU further reduced : the ordinary minute subdivisions of syste- 

 matizing geologists are wholly inapplicable to such accumulations 

 as these. 



Prom this it is evident that the Antwerp sections fully satisfy the 

 inquiry as to relative age. The Scaldesien division there is younger 

 than the Diestien, as it has been accumulated over it. So likewise 

 the upper Scaldesien must be younger than the lower ; but this is 

 merely relative age in respect of rearrangement. The corresponding 

 conditions on the English and Belgian areas of the Crag sea are the 

 Eed Crag and the Scaldesien ; both are " remanie " accumulations. 

 The diiference which these present in respect of the marine fauna 

 they contain, is not of much amount numerically, and, viewed in detail, 

 it is just such as would arise from the diiferent sources whence each 

 was derived. The Red Crag was from the break up of a neighbour- 

 ing Bryozoan sea-zone, the Scaldesien from Ooz,e depths. Any com- 

 parison of the fossil contents of the " Coralline Crag " and of the 

 "Crag noir" must be subject to the consideration of differences 

 which result from depth and condition of sea-bed. Erom the nature 

 of the question, therefore, a percentage calculation for determining 

 relative age is inapplicable with respect to the component parts of 

 the English and Belgian Crag, or even of one part with another of 

 the same series. 



The fossils of the Systeme Diestien are proper to it ; and from 

 them may be inferred the condition of that part of the Crag sea for 

 that particular time. The fossils of the Scaldesien beds are wholly 

 extraneous to them, belonging to all regions of depth, and all 

 periods of the Crag formation — from them no guidance in geological 

 chronology can be derived. 



III. Conditions op Ckag-Sea. Aeea. 



By combining the results obtainable from the East Anglian and 

 Belgian Crag beds, some general views may be deduced as to the 

 Crag sea, both physical (1) and zoological (2). 



1. Physical Features. — Along the lower courses of the Orwell and 

 Deben, and thence towards Orford and Aldborough, the Crag beds 

 occupy an old depression. The greatest extension which the sea 

 had here was by Bentley, Ipswich, and Woodbridge. The Eed Crag 

 of these places being a true sub-littoral accumulation. 



Corresponding beds, as to age, occur in two other old depressions, 

 those of the Blyth and the Yare. At Yarmouth it may be inferred 

 that there is a considerable thickness of Crag (Prestwich, Quart. 

 Journ. Geol. Soc. vol. xvi. p. 449). Finally, a sea-bed of the same 

 age is seen at Mundesley. In tracing the outline of the Crag sea, it 

 may safely be made to include a rather wide area, about the lower 

 courses of the Waveney, Yare, and Bure. 



