1866.] GODWIN-AUSTEN — BELGIAN TERTIAKIES. 239 



Rivers discharged at several places, bringing down the land and 

 freshwater shells of the period into the Crag sea, of which forms the 

 Unio litoralis and Cyrena consobrina are the best guides. On one 

 side of this sea, the Grays beds represent the purely fluviatile or 

 estuarine beds of the great tributary of the Thames valley ; whilst the 

 Norwich beds and those of Kelsey belong to the fluvio-marine facies, 

 in connection with the streams or rivers of the Yare and Humber. 



North of the East Anghan area the Crag sea is indicated at inter- 

 vals, as at Bridlington and Stains (Aberdeenshire), and by its fossils 

 over the bed of the North Sea. 



In addition to the conditions here given, we have on the English 

 side of the area the Coralline Crag, or Bryozoan facies of its sea-bed. 



From near Maastricht the Crag beds extend beneath newer accu- 

 mulations into Guelderland (Winterswyk, Bekken)*. 



The sheUy sands which in North Holland occur beneath the Dune- 

 sand, Polder-, and Peaty-beds, are, undoubtedly, of the Crag Period, 

 and the same sea-bed is met with in Segeberg, Liineberg, and Sylt ; 

 but it does not extend eastwards into the Baltic area, and that 

 depression owes its origin to a subsidence or depression of the great 

 Scandinavian mass, the line of which, very probably, is that of the 

 deep-sea soundings, and which accordinglv has been taken (vide 

 Map, fig. 2). 



The Crag sea opened out northwards. On the extreme south its 

 condition is indicated, first, by the great breadth of the sand-zone, 

 eKtending the whole length of the axis of Artois, and the Ardennes 

 chain; and next by the transport, along a line of coast, of the 

 flint-gravel and shingle, which must necessarily have been derived 

 from the English side of the area. As these materials occur from 

 the basement bed to the uppermost, such a coast-line must have 

 been continued during the whole of the Crag-sea period, as a limit 

 on the South. Structurally, the limitation was dependent on the 

 extension of the axis of Artois, and of our own Wealden elevation. 

 The Sangatte section shows that this barrier was maintained until 

 the close of the Glacial Period f. 



At this time the Northern hemisphere presented a broad belt of 

 circumpolar land, and these geographical arrangements influenced 

 the character of the Crag-sea fauna. 



Such a communication as the present does not admit of a detailed 

 analysis of the Crag- sea fauna in respect of its origin, though the 

 materials are amply sufficient, but the subject may be alluded to, 

 inasmuch as the peculiarities can alone be explained by reference to 

 bygone geographical arrangements. 



What these must have been is given in the accompanying small 

 sketch-map, which shows why the Crag Molluscan fauna, which is 

 wholly Atlantic, like that of the synchronous sea-beds of Selsey, the 

 Cotentin, the Faluns of Touraine and Bordeaux, &c., should dift'er 

 from these last to so great an extent. The Crag-sea area included 

 the representatives of two distinct Atlantic provinces, the Boreal or 



* Staring. Bodem van Nederland. vol. ii. p. 284. 



t See Nat. Hist, of European Seas, p. 286, and Map II. 



