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CHAPTER XVII. 



PLIOCENE STRATA. 



THE PLIOCENE STRATA, or Newer Tertiary beds, form the 

 succeeding division of the Tertiary series, and in Eng- 

 land are represented by the various subdivisions of the 

 CRAG of Suffolk and Norfolk. Resting, as these strata 

 generally do, on an eroded surface of the London Clay, or 

 more rarely, on the Chalk, their lower boundary is suf- 

 ficiently clear ; but the same is not the case with the 

 upper limit of the Crag series, about which diversities 

 of opinion exist, arising, no doubt, from the circumstance 

 that it is absolutely indefinable, there being a kind of 

 passage from the uppermost beds of Crag into over- 

 lying strata partly of drifts and glacial detritus. The 

 whole series of Crags and disputed Crags is, indeed, 

 probably not more than from 120 to 150 feet thick, 

 and they make no decided mark on the physical geo- 

 graphy of the country, though important in other points 

 of view. After much consideration I incline, for the 

 present, to restrict the term Crag to the following 

 subdivisions : 



Norwich Crag : fluvio-marine. 

 Bed Crag. "l Suffolk . 



Coralline Crag.J 



The Coralline or White Crag lies on the London 

 Clay in Suffolk, and consists of a few patches found in 



