208 INCREASING COLD SHOWN BY CHAP. xn. 



we advance into more southern latitudes approaching the 

 50th parallel of latitude in Europe, and the 40th in North 

 America, this disturbing cause ceases to oppose a bar to our 

 inquiries ; but even then, in consequence of the fragmentary 

 nature of all geological annals, our progress is inevitably slow 

 in constructing any thing like a connected chain of history, 

 which can only be effected by bringing the links of the chain 

 found in one area to supply the information which is wanting 

 in another. 



The least interrupted series of consecutive documents to 

 which we can refer in the British Islands, when we desire to 

 connect the tertiary with the post-tertiary periods, are found 

 in the counties of Norfolk, Suffolk, and Essex ; and I shall 

 speak of them in this chapter, as they have a direct bearing 

 on the relations of the human and glacial periods, which will 

 be the subject of several of the following chapters. The 

 fossil shells of the deposits in question clearly point to a 

 gradual refrigeration of climate, from a temperature some 

 what warmer than that now prevailing in our latitudes to one 

 of intense cold ; and the successive steps which have marked 

 the coming on of the increasing cold are matters of no small 

 geological interest. 



It will be seen in the Table at p. 7, that next before the 

 post-tertiary period stands the pliocene, divided into the 

 older and newer. The shelly and sandy beds representing 

 these periods in Norfolk and Suffolk are termed provincially 

 Crag, having under that name been long used in agriculture 

 to fertilise soils deficient in calcareous matter, or to render 

 them less stiff and impervious. In Suffolk, the older pliocene 

 strata called Crag are divisible into the Coralline and the 

 Eed Crags, the former being the older of the two. In Norfolk, 

 a more modern formation, commonly termed the 6 Norwich,' 

 or sometimes the < mammalif erous ' Crag, which is referable to 

 the newer pliocene period, occupies large areas. 



