676 PROCEEDINGS OF THE BALTIMORE MEETING 



Miocene Formations 



In Maryland the divisions of the Miocene are three in number — Calvert, 

 Choptank, and Saint Marys — and these with slight modifications extend across 

 the Potomac river, and have been recognized in Virginia by their character- 

 istic fossils and also similar lithologic materials. Besides, in Virginia a new 

 formation makes its appearance that does not appear at the surface in Mary- 

 land, though it may be present in the eastern part of the state beneath the 

 thick cover of Pleistocene materials. This is the Yorktown formation, so well 

 exposed in the vicinity of Yorktown, on the York river. Of the three Miocene 

 formations that extend across the Potomac river from Maryland, two of them — 

 the Calvert and the Choptank — gradually disappear toward the southern part 

 of the state, due to overlap or to non-deposition. The latter seems to be the 

 case from what has been determined in North Carolina, where the Cretaceous 

 is found immediately beneath the Saint Marys formation. In North Carolina 

 we have three Miocene formations — the Saint Marys, which extends in an 

 unbroken band from Maryland entirely across the state of Virginia ; the York- 

 town, which first appears as a surface formation in the vicinity of the York 

 river, in Virginia, and which is continuous to the vicinity of the Neuse river, in 

 North Carolina, though concealed in greater part in the interstream areas, and 

 the Duplin, which occurs in isolated areas in the southern portion of the state 

 and under similar conditions in the northern part of South Carolina. The 

 Saint Marys formation, in the northern part of the state, rests on the Cre- 

 taceous or the crystalline rocks. Near Halifax a stratum containing well pre- 

 served molluscan shells is found in immediate contact with the decayed crys- 

 tallines of the Piedmont plateau. Along the Tar river many exposures show 

 the Saint Marys formation in contact with the lowest member of the Cre- 

 taceous. North of the Neuse river, in North Carolina and all through Virginia, 

 the Saint Marys formation seems to be continuous and is exposed in the valley 

 of each of the major streams. South of the Neuse river it is doubtfully repre- 

 sented in only a few localities, and there occurs as isolated patches of small 

 extent. 



The Yorktown formation makes its appearance in the vicinity of the York 

 river in Virginia, and from there extends southward as a continuous band to 

 the Neuse river, and throughout this belt rests on the Saint Marys formation 

 with no marked unconformity. Tracing the deposit over a considerable area, 

 however, it is found to be unconformable, and the basal stratum, consisting of 

 fragmental shells of beach origin, indicates an uplift of the region before the 

 deposition of the Yorktown. The fact that we find the Saint Marys present so 

 extensively to the north of the Neuse river and find only patches of it south- 

 ward would seem to indicate its original distribution as a continuous forma- 

 tion over a large part of the Coastal plain. Further, the fact that we now 

 find the Yorktown resting directly on strata of Eocene age in the vicinity of 

 Newbern, between the Trent and Neuse rivers, implies an erosion interval of 

 considerable duration after the deposition of the Saint Marys and before the 

 laying down of the Yorktown strata. 



The Yorktown, in its turn, south of the Neuse river, suffered much erosion 

 prior to the opening of the Pliocene period, and perhaps since the Pliocene as 

 well. The Duplin formation is found in isolated areas along the Cape Fear 



