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 Red Crags, the former being the older of the two. In Norfolk, a more modern formation, commonly termed the 'Norwich,' or sometimes the 'mammaliferous' Crag, which is referable to the newer pliocene period, occupies large areas.
