CHAP. xii. NORFOLK AND SUFFOLK TERTIAKIES. 211 



not thrown up from deep water. Yet the northern character 

 of the Norwich Crag is not fully shown by simply saying that 

 it contains twelve northern species, now no longer found in 

 British seas, since several boreal shells which still linger in 

 the Scottish deeps do not abound there as they did in the 

 latter days of the Crag period. It is the predominance of 

 certain genera and species which satisfies the mind of a 

 conch ologist as to the arctic character of the Norwich Crag. 

 In like manner, it is the presence of such genera as Pyrula, 

 Columbella, Terebra, Cassidaria, Pholadomya, Lingula, 

 Discina, and others which give a southern aspect to the 

 Coralline Crag shells. 



The cold, which had gone on increasing from the time of 

 the Coralline to that of the Norwich Crag, continued, though 

 not perhaps without some oscillations of temperature, to 

 become more and more severe after the accumulation of the 

 Norwich Crag, until it reached its maximum in what has been 

 called the glacial epoch. The marine fauna of this last 

 period contains, both in Ireland and Scotland, recent species 

 of mollusca now living in Greenland and other seas far north 

 of the areas where we find their remains in a fossil state. 



The refrigeration of climate from the time of the older 

 to that of the newer Pliocene strata is not now announced 

 for the first time, as it was inferred from a study of the Crag 

 shells in 1846 by the late Edward Forbes.* 



The most southern point to which the marine beds of the 

 Norwich Crag have yet been traced is at Chillesford, near 

 Woodb ridge, in Suffolk, about eighty miles north-east of 

 London, where, as Messrs. Prestwich and Searles Wood have 

 pointed out,f they exhibit decided marks of having been 

 deposited in a sea of a much lower temperature than that now 

 prevailing in the same latitude. Out of twenty-three shells 



* Manual of Geological Survey, f Quarterly Geological Journal, 



London, 1846, p. 391. 1849, vol. v. p. 345. 



P 2 



