.0                                                                              
   1  Million years.                                                            
                                                                                
   2  Age of upper parts of uppermost Tertiary units is problematic.  These     
parts have historically been assigned to the Pliocene.  Successive reductions   
in radiometric age of the base of the Pliocene in Europe to 7 m.y. (Lambert,    
1971) or 5 m.y. (Berggren, 1972) places a Pliocene age in question, though top  
beds of the formations have not been dated.