1895- 



THE GEOLOGY OF IPSWICH. 



175 



line Crag, and resting unconformably on it or on the London Clay, 

 follow false-bedded marine sands, with fossils pointing to shallow water 

 and to a sea getting colder and colder as time goes on. This gradual 

 climatic change is well exhibited by the various sections around Ipswich. 

 At Walton, for instance, the oldest part of the Red Crag contains fossils 

 indicating a climate not greatly colder than that of the CoraUine 

 Crag period. At Butley the newer part of the Red Crag yields more 

 boreal species ; while at Chillesford the arctic mollusca form a still 

 larger proportion of the whole. Near Cromer, on the Norfolk coast 

 — which will be visited by one of the excursions — a later stage, the 

 Weybourn Crag, is represented. This crag, though still full of charac- 

 teristic Pliocene mollusca, yields a very large percentage of arctic forms. 

 The gradual refrigeration of the climate in the course of time, the 

 disappearance of the southern and extinct forms, and the incoming of 

 the Arctic species, is well exhibited in a table of the marine mollusca 

 drawn up some years since, and here reproduced : — 



The evidence yielded by the marine fauna of the Pliocene period 

 does not tally, however, with that of the land and freshwater species. 

 It is often stated that after the gradual refrigeration of the climate 

 there was again a warm period, before the commencement of the 

 actual glaciation of East Anglia, and that this mild interval is repre- 

 sented by the Cromer Forest-bed with its temperate fauna and flora. 

 Of this Pliocene alternation of climates I do not think there is any 

 real evidence. The Newer Pliocene marine fauna, from whatever 

 horizon it is obtained, is always somewhat arctic, the whales and the 

 few marine mollusca of the Cromer Forest-bed being just as boreal 

 as those of the Crag below. The Pliocene land animals and plants, 

 on the other hand, from every horizon are, with one or two exceptions, 

 temperate species. The necessity, so often noticed by geologists, for 

 two parallel classifications for the marine and for the land faunas, is 

 nowhere more marked than in the Newer Pliocene period, and in 

 describing the deposits I have been obliged to keep the parallel faunas 

 quite distinct (4). 



The reason for this singular discordance between the apparent 

 climatic conditions as shown by the marine animals and that evidenced 

 by the land and freshwater fauna and flora is probably very simple 

 and due to a slight change in the physical geography. During the 

 deposition of the Coralline Crag the sea was open to the south, and 

 everything points to a genial climate. But when the shoaler water 

 Newer Pliocene was being deposited, land connected England with 



