Cxliv CORRELATION OF MARYLAND MIOCENE 



Gulf Coast, While faint traces remain, in the mechanically mixed marls 

 of southern New Jersey, of the former presence of Oligocene sediments, 

 it is only by the occurrence of a few Oligocene species, mixed with much 

 more numerous Chesapeake forms, that this may be detected. South of 

 New Jersey no trace of the whole Oligocene series may be recognized, as 

 far as now known, north of Georgia. Nor is there described any remnant 

 of the uppermost Eocene as represented in the Gulf column of formations. 

 The beginnings of the Chesapeake in Maryland and Virginia are marked 

 by the prevalence of beds of diatomaceous earth. Otherwise there is 

 little that is distinctive in the successive beds of clay, sand and gray or 

 bluish marl which make up the bulk of the series, divided, on the basis 

 of its fauna, into three formations in Maryland, known as the Calvert, 

 Choptank and St. Mary's. In Virginia we are greatly in need of more 

 stratigraphical information but it is believed that the older beds in the 

 main lie to the north and west, dipping southeasterly 8 to 10 feet per 

 mile, and, as at Petersburg, are practically similar to the Maryland 

 deposits. Passing to the southeast, beds higher in the scale are encoun- 

 tered, though the fauna is still very similar to that of Maryland. Finally 

 on the southeastern border at the sea, along the York river and at various 

 other localities we find beds of marl of a much lighter color, tinted 

 yellow by the presence of iron oxide, and containing a larger proportion 

 of recent forms, together with a still notable proportion of those which 

 occur in the Maryland beds. These newer sediments culminate near 

 Suffolk and about the upper Nansemond river district in the most recent 

 beds of all, on the top of which, in the basin of the Great Dismal Swamp, 

 have been collected mixed with unconsolidated Miocene marl, a few 

 characteristic species of the Southern Pliocene. In Virginia and Mary- 

 land we appear to have the basis of material necessary to trace the 

 development of a normally evolving fauna of a single origin, but when 

 we reach North Carolina we come upon an association of species in the 

 upper or Duplin Miocene, in which the introduction of a new factor is 

 manifest. This is a change of fauna due (as in the recent fauna of the 

 coast) not to earlier or later development, but to modifications due to 

 temperature and the environment, which have produced an assemblage, 

 perhaps simultaneously existing with that of Suffolk, Virginia, but 

 of an obviously more southern character. At present tlie promontory of 



