200 OLDER PLIOCENE STRATA. [Ch. XIII. 



per cent, of extinct species instead of 11, as in the Norwich beds on 

 the Yare. Of the whole 64 shells, 36 are common to the Norwich 

 Crag proper, and 12 are peculiar to Bridlington, or were not pre- 

 viously known in any pliocene or glacial deposits in Great Britain. 

 What is most remarkable is the fact, that of the 60 species which 

 remain after abstracting the extinct forms, no less than 30 are inhabit- 

 ants of the Arctic regions, none of them extending southward to the 

 British seas. This is the more singular when we consider that Brid- 

 lington is situated in lat. 54° 1ST. It will be seen in the next chapter 

 that the cold came on gradually, beginning when the White Crag was 

 formed, and increasing in the period of the Red Crag, and still more 

 in that of the Norwich formation, during which there may have been 

 several oscillations of temperature. The refrigeration seems to have 

 reached its maximum, and to have been developed most extensively 

 in Europe in Post-pliocene times. It may, no doubt, be said that the 

 shells of Moel Tryfaen above mentioned, found at a height of nearly 

 1400 feet above the sea, and in lat. 53° N., or nearly the same as that 

 of Bridlington, do not imply so great a cold as the latter, as they 

 only contain 11 shells in 54 of exclusively Arctic character, or only 

 one-fifth .of the whole number of species, instead of nearly half, as in 

 the case of Bridlington. But the fauna of Moel Tryfaen does not 

 illustrate the extreme cold of the glacial period like the beds of Errol 

 and Elie, on the borders of the Tay and Forth. (See p. 153.) 



OLDER PLIOCENE STRATA. 



Red Crag of Suffolk. — The Crag of Suffolk, as already mentioned, 

 is divisible into the Upper or Red, and the Lower or White Crag.* 



These deposits, according to the late E. Forbes, appear by their 

 imbedded shells to have been formed in a sea of moderate depth, 

 usually from 15 to 25 fathoms, but in some few spots perhaps deeper. 

 Yet they cannot be called littoral, because the fauna is such as may 

 have extended 40 or 50 miles from land. The Upper or Red Crag 

 consists chiefly of quartzose sand, with an occasional intermixture of 

 shells, for the most part rolled, and sometimes comminuted. It is 

 distinguished by the deep ferruginous or ochreous color, both of its 

 sands and shells, while the Older Crag, commonly called the Coralline, 

 is white. Both formations are of moderate thickness ; the Red Crag 

 rarely exceeding 40, and the Coralline seldom amounting to 20 feet. 

 But their importance is not to be estimated by the density of the 

 mass of strata or its geographical extent, but by the extraordinary 

 richness of its organic remains, belonging to a very peculiar type, 

 which seems to characterize the state of the living creation in the 

 north of Europe during the Older Pliocene era. 



* See paper by E. Charles worth, Esq. ; London and Ed. Phil. Mag., No. xxxviii. 

 p. 81, Aug. 1835. , . 



