157 MURFREESBORO STAGE — OLSSON 



clays found beneath the Yorktown stage on the James river 

 belong to the Murfreesboro, as do the beds of similar lithology 

 and stratigraphic position in northern and central North Caro- 

 lina, as for examble at Halifax, Greenville, etc. 



This stage has in general been misinterpreted, and differ- 

 ent parts correlated with different portions of the Miocene series. 

 The presence of beds of diatomaceous earth, seemingly in a con- 

 tinuous belt extending south from Maryland (as for example at 

 Petersburg, Va. ), and apparently closely associated with these 

 beds, has led to their direct correlation with the similar deposits 

 of the Calvert stage of Maryland. The evidence furnished by 

 the more wide-spread and better known molluscan fauna is more 

 trustworthy and should therefore be given more consideration 

 than the presence of diatomaceous beds which might as well as 

 not have been developed at different periods. 



Heilprin* in 1884, although recognizing an intimate relation 

 of the Virginian fossils to each other and therefore indicating a 

 nearly uniform age, still held to his anomalous view, earlier ex- 

 pressed, of the continuation of his Marylandian or older Miocene 

 south into Virginia and North Carolina, representing there the 

 northern faunal horizon. He attributed this seeming dif- 

 ference in characteristics to ' 'imperfect observation or lack of ob- 

 servation." In 1904, Dallf compared the Maryland Miocene 

 with other well-known localities. On the basis of the percent- 

 age of recent species, these localities were arranged in a series to 

 show their relative ages. In this scheme, the Petersburg beds 

 (included now in the Murfreesboro stage) were considered as be- 

 ing very old and beneath the Calvert or synchronous with it. 

 For various reasons, final correlation by the percentage of the 

 molluscan species which have survived to the present'day cannot 

 be relied upon for exact and detailed work. This principle is of 



Contributions to the Tertiary Geology and Paleontology of the Uuited 

 States, pp. 15, 16. 



fMaryland Geological Survey, Miocene volume, pp. cxlvii, cxlviii. 



