446 PREHISTORIC E UR OPE. 



occupy a shallow basin scooped out of older deposits. Accord- 

 ing to Mr. Skertchly the oldest of the true Fen-beds are 

 certain unfossiliferous gravels, which are found almost every- 

 where paving the bottom of the ancient silted-up basin, and 

 extending more or less continuously along the margin of the 

 Fenland, where, according to the same writer, they evidently 

 indicate a former line of beach. The beds above these beach- 

 and floor -gravels consist of silt, peat, and shell -marl, which 

 interosculate in such a manner as to show that they are fre- 

 quently of contemporaneous origin, that is to say, that the peat 

 and shell-marl in one place have been formed at the same time 

 that silt was accumulating elsewhere. Thus it is very difficult 

 or impossible to correlate the beds in one district with those 

 which occur in other places. All that can be said is that the 

 formation of peat and silt has progressed contemporaneously and 

 alternately throughout a long period of time, and some idea of 

 the lapse of time required for the accumulation of the Fen-beds 

 may be gathered from examining a few sections taken at different 

 places. But before doing so it is necessary to inquire into the 

 relation which the true Fen-beds bear to the glacial deposits 

 of that region. The basin in which the former lie has been 

 excavated partly in Oolitic strata and partly in boulder-clay. 

 This boulder- clay is the houe glaciaire of the great ice -sheet 

 which, as I have already stated, there are good grounds for 

 believing, flowed south as far as the valley of the Thames. It 

 belongs to the climax of the Glacial Period, and is therefore of 

 vastly greater antiquity than any portion of the Fen-beds, how- 

 ever ancient these may be. Here and there the level surface of 

 the Fenland is broken by the presence of slight hills and rising 

 grounds, which form islands, as it were, in the wide expanse. 

 These islands are composed of ancient river- and estuarine- 

 gravels resting upon boulder-clay ; and they indicate, as Mr. 

 Skertchly remarks, the former existence of a land higher than 

 the present, when the coast-line was not so far east. The gravels 

 have yielded Palaeolithic implements and remains of the mam- 

 malia characteristic of Pleistocene times. It is quite clear, then, 



