36 TJie Geology of Cambridgeshire 



possibly to the M. cortnif/uinum zone, but no exposures of 

 either can be definitely recognized within the county. 



Eastward in Suffolk and in Norfolk the higher zones come 

 on in turn, and there is no reason for doubting that the whole 

 series was deposited over Cambridge. All has now gone, and 

 moreover, all had gone before the next succeeding deposit, 

 the Boulder-clay, was accumulated. 



EOCENE RECENT. 



What occurred in the Cambridgeshire area in the interval 

 between Chalk and Boulder-clay we may never know, and at 

 present can hardly conjecture. Certain it is, however, that 

 a period of earth movement affected all England at the end 

 of Cretaceous time, and from being the bottom of a land- 

 locked gulf our area must have passed into the condition of 

 a coastal plain which bordered some vast continent stretching 

 far away to the north-west. In Eocene time a great river 

 from the west brought down the various deposits of the 

 London and Hampshire basins, and a slight sinking about 

 its estuary allowed the tides to bring Bagshot sands within 

 some fifteen miles of Cambridge. 



The Oligocene and Miocene were periods of great dis- 

 turbance, and the earth movements in giving the Mesozoic 

 rocks of England their present strike must have produced 

 profound changes in the pre-existing lines of drainage, and 

 may have given the dip streams their present courses. 



Pliocene time brought with it a certain amount of sub- 

 sidence, and a North Sea opening northward soon washed 

 over the Eastern Counties. A river from the south, an 

 ancestor of the present Rhine, brought down silt to be 

 deposited in that sea, and the Crags of the East Coast were 

 formed as shell banks beyond its delta, each series a little 

 further to the north than its predecessors. 



Meanwhile the climate had been steadily becoming colder, 

 and by the end of the Pliocene period an almost Arctic flora 

 and fauna was living on the present shores of East Anglia. 



