cxlviii 



CORRELATION OF MARYLAND MIOCENE 



It is likely that complete collections from each of the Virginia locali- 

 ties might bring about a change of one or two per cent in the proportion 

 of surviving species, so that too much stress should not be laid on small 

 differences of this kind ; also, that, in the warmer regions, the proba- 

 bilities of survival among the smaller species are greater than in colder 

 waters. Making allowances for these factors it is probable that the age 

 (in descending order), of the several horizons, as measured by their 

 percentage of surviving species, would not differ greatly from the follow- 

 ing scheme: 



Duplin. 

 Suffolk. 

 Yorktown. 

 Alum Bluff. 

 St. Mary's. 

 rChoptank. 

 [James Eiver. 

 rCalvert. 

 [Petersburg. 

 Taking the three subsidiary horizons of the ]\Iaryland Miocene, the 

 percentage of species in each of the cited Virginia horizons common to 

 each of the Maryland horizons is as follows: 



From this it may be concluded that the connection between the Mary- 

 land and Virginia Miocene, as well as between the several horizons in 

 each state, is very intimate, and while the groups may be divided the 

 divisions are less fundamental than the general unity of the Chesapeake 

 as a whole compared with, for instance, the Duplin Miocene, which has 

 in common with the Suffolk beds only ten per cent of common species, 

 while of the non-peculiar species of the far more distant Chesapeake of 

 Florida 39 per cent are common to the Chesapeake of Maryland. 



