A) The following 7 categories provide ranks for the dating control in cores with
   continuous sedimentation.                                                    
1   Bracketing dates (mainly radiocarbon) within                                
    2000 yrs of selected date, i.e. 6000 yr B.P.                                
2   Bracketing dates, both within 2000 years and                                
    the other within 4000 years of the selected                                 
    date.                                                                       
3   Bracketing dates, one within 4000 years of                                  
    of selected date.                                                           
4   Bracketing dates, one within 4000 years and                                 
    the other within 6000 years of the selected                                 
    date.  The second date can be the top of                                    
    the core with an assigned date of 0 yr B.P.                                 
5   Bracketing dates within 6000 years of the                                   
    selected date.                                                              
6   Bracketing dates, one within 6000 years and                                 
    the other within 8000 yers of the selected                                  
    date.                                                                       
7   Undated at selected date (i.e. 6000 yr B.P.):                               
    either no dates in core, no bracketing dates,                               
    or no top to core and no date within 8000                                   
    years of the selected date.                                                 
B) The ranking of the dating control for the European pollen data was done by   
   B. Huntley before the above system was established. The ranks for the        
   European data include 4 categories that are approximately similar to the     
   above categories in the following way: 1=1 above, 2=2 above, 3=3 above, and  
   4=7 above.                                                                   
C) For ranking the dating control in sites with discontinuous samples (e.g.     
   shoreline samples for lakes, isolated peats, packrat middens), the categories
   used require single radiocarbon dates within 1) 250 years, 2) 500 years,     
   3) 750 years, 4) 1000 years, 5) 1250 years, 6) 2000 years, and 7) greater    
   than 2000 years of the date being mapped (e.g. 6000 yr B.P.)