CHAPTER V 



CAINOZOIC FAUNAS (PLS. xv. AND xvi.) 

 (A) GENERAL ACCOUNT 



FOSSILIFEROUS Tertiary deposits in Britain are 

 not only small in bulk and restricted in distribution, 

 but show considerable monotony in formation and 

 composition. Marine strata constitute a relatively small 

 proportion, and always show signs of shallow, almost lit- 

 toral, origin. Permanent presence of an important area 

 of land since Cretaceous times ensured a plentiful supply 

 of detrital matter ; since the two main areas of Lower 

 Tertiary sedimentation (the London and Hampshire 

 Basins) corresponded with the estuaries of drainage- 

 systems, sand, but especially clay, are the chief deposits. 

 Such limestones as occur are either marine shell-beaches 

 or fresh-water lake-marl. Typical Pliocene strata, though 

 less argillaceous than those of the Eocene, were even 

 more definitely coastal in formation. 



Hence the British record of Cainozoic faunas is far 

 from representative. Within its limited range it is often 

 extraordinarily full. Mollusca in particular occur in 

 immense numbers. But as a qualifying factor there 

 has to be recorded the existence of such deposits as the 

 Reading Clays and Bagshot Sands, which are almost 

 absolutely unfossiliferous. The absence of any definite 

 Miocene strata, and the largely lacustrine origin of much 

 of the Oligocene, further interfere with the continuity of 



the faunal record. 



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