30 



Bulletin 39 



al formations or stages is frequently known as the Chesapeake 

 Miocene or Chesapeake series, and the lower consisting solely of 

 the Alum Bluff formation, may be designated for sake of discus- 

 sion, the Alum Bluff series. These Miocene formations or stages 

 are the following: 



pa 



a 

 o 



upper 



* >l< 



Middle 



Chesapeake Series 



* 



Alum Bluff Series 



Lower 



Yorktown, Duplin Stages 

 Murfreesboro Stage ^ 



^ ^j^ ^ ^ 



St. Mary's Stage 

 Choptank Stage 

 Calvert Stage 



^< >|< * * * 



Alum Shoal River marl 

 Bluff 



Stage Oak Grove marl 

 Chipola marl 



This tv\^o-fold division is a very natural one. Each series 

 represents a distinct trangression of the Miocene sea over parts of 

 the Atlantic coastal plain, that of the Chesapeake being the 

 more extensive. In Florida, w^here the Chesapeake Miocene is 

 sometim.es found resting upon the Alum Bluff beds, as at Alum 

 and Jackson Bluffs, the contact is seen to be an erosional uncon- 

 formity. At these localities, the Chesapeake Miocene is equiva- 

 lent to the Murfreesboro stage or formation of Virginia and 

 North Carolina, and hence the time interval represented by this 

 break is equivalent to the Lower Chesapeake or the Marylandian 

 Miocene. Dall,* who has paid special attention to the relations 

 of the Alum Bluff and the Chesapeake series, both stratigraphi- 

 cally, and paleontologically, characterizes this break as "the 

 most sudden, emphatic, distinct in the whole post- Cretaceous his- 



* Trans, Wagner Free Inst., 1903, p. 1594 



