PEESTWICH — CRAG-BEDS OF STTFFOLK AND NORFOLK. 



479 



chalk-flints from neighbouriDg shores shows transport by ice. The 

 many fragments of secondary rocks and of mountain-limestone in 

 the Red and Norwich Crags were probably brought down by river- 

 action or river-ice. jSTor is the increase in the northern species of 

 shells very great in ascending through the Norwich Crag, though 

 the number of individuals increases considerably, and a number of 

 southern species become extinct. At the same time it is sing-ular 

 that so many Coralline-Crag species, mostly of British and Mediter- 

 ranean forms, should reappear in the last or uppermost stage of the 

 Crag at Aldeby. 



This conclusion is in accordance with the land-fauna and flora we 

 find flourishing subsequent to the Norwich Crag. The winter cold 

 may have been greater ; but otherwise the climate seems to have 

 been a moderately temperate one. In the Forest-bed the vegeta- 

 tion, whether as regards the species or the size of the trees, is far 

 from indicating a severe climate. Nor do we find any of the Mam- 

 malia which indicate extreme cold. The Mastodon no longer ap- 

 pears ; but an Elephant, a Bear, and two Deer of the Crag period 

 survive. "With these, however, some of the animals of the postglacial 

 period appear, showing probably the setting in of colder conditions 

 there or further north. In the Westleton shingle we get the drifted 

 remains of the same vegetation, and the same land and freshwater 

 shells ; but these latter are of a character common to all northern 

 and temperate Europe. The marine MoUusean fauna now becomes 

 poorer, but still without any decidedly marked northern characters ; 

 nor are any foreign boulders found — nothing but drifted pebbles 

 carried possibly along a shore-line. Nevertheless we have in this 

 series the nearest known approach to the glacial period, which set 

 in immediately afterwards with a rigour and intensity denoting, I ap- 

 prehend, causes of an entirely different order from those, the effects 

 of which, up to this time, may be attributed to the known and 

 assignable influence of land configuration and oceanic currents. 



