Ch. XIII.] SUCCESSIVE KEFRIGERATION OF CLIMATE. 205 



of a species of Pyrula, supposed by Mr. Wood to be identical with 

 P. reticulata (fig. 158), now living in the Indian Ocean. A genus 

 also of echinoderms, called by Professor Forbes Temnechinus (fig. 

 159), is peculiar to the Eed and Coralline Crag of Suffolk. The only 

 species now living occur in the Indian Ocean. • 



One of the most interesting conclusions deduced from a careful 

 comparison of the shells of these British Older Pliocene strata and 

 the fauna of our present seas, has been pointed out by Professor E. 

 Forbes. It appears that, during the glacial period, a period interme- 

 diate, as we have seen, between that of the crag and our own time, 

 many shells, previously established in the temperate zone, retreated 

 southward to avoid an uncongenial climate. The Professor has given 

 a list of fifty shells which inhabited the British seas while the Coral- 

 line and Eed Crag were forming, and which, though now living in 

 our seas, are all wanting in the glacial deposits. They must there- 

 fore, after their migration to the south, which took place during the 

 glacial period, have made their way northward again. In corrobora- 

 tion of these views, it is stated that all these fifty species occur fossil 

 in the Newer Pliocene strata of Sicily, Southern Italy, and the Gre- 

 cian Archipelago, where they may have enjoyed, during the era of 

 floating icebergs, a climate resembling that now prevailing in higher 

 European latitudes.'" 



The following tables have been drawn up for me by Mr. Samuel P. 

 Woodward, showing- the results of a comparison of the lists of Crag 

 shells described by Mr. Searles Wood in his excellent monograph on 

 the fossil testacea of the British Pliocene formations. The list of the 

 Xorwich Crag shells has been corrected and enlarged by Mr. Wood- 

 ward himself. They exhibit clear evidence of a gradual refrigeration 

 of climate, which went on in the area of England from the time of 

 the older to that of the most modern Pliocene strata, a refrigeration 

 which has already been inferred from an examination of the Crag shells 

 in 1846 by the late Edward Forbes.f 



Number of known Species of Marine Testacea in the three English 

 Pliocene Deposits, called the Norwich, the Red, and the Coralline 

 Crags.% 



Brachiopoda, .... 6 



Conchifera, ------ 210 



Gasteropoda, ..... 220 



Total, - - 436 : 



* E. Forbes, Mem. Geol. Survey Gt. Brit., vol. i. p. 386. 

 •f Mem. of Geol. Survey, London, 1846, p. 391. 



% The 25 shells peculiar to Bridlington (p. 199) are not included in the Norwich 

 Crass; shells of these tables. 



