RECENT INVESTIGATION OF COASTAL PLAIN FORMATIONS 647 



General Characteristics of the Formations 



The progress of the investigation of the formations of the middle and north- 

 ern Atlantic Coastal Plain region furnishes little by little a clearer interpreta- 

 tion of the geology of that area. The deposits as a whole have been but little 

 changed since they were originally laid down along the coastal border, but the 

 strata present much complexity due to the variation in the angle and direction 

 of tilting during the successive oscillations of the sea floor. The sediments in 

 general form a series of thin sheets which are inclined seaward, so that suc- 

 cessively later formations are encountered in passing from the inland border 

 of the region toward the coast, yet at no place accessible to our study do we 

 find a complete sequence of deposits, although sedimentation must have been 

 continuous over a large part of the continental shelf. The incompleteness, 

 therefore, must be regarded as a purely marginal condition due to the trans- 

 gressions and retrogressions of the sea along the coastal border. 



The correlation table given on the accompanying plate shows the relations of 

 the several formations throughout the northern and middle Atlantic Coastal 

 plain and their approximate equivalents in the eastern Gulf region. 



Cretaceous 



The Cretaceous formations constitute the basal deposits of the Coastal Plain 

 series along the line of outcrop. Well borings throughout the district have not 

 afforded strata of earlier age, although they may exist to the eastward toward 

 the margin of the continental shelf. 



LOWER CRETACEOUS 



Deposits of Lower Cretaceous age are most extensively developed in Mary- 

 land and northern Virginia, where the Patuxent (arkosic sands, gravels, clays), 

 Arundel (clays, lignites, carbonate of iron concretions), and Patapsco (varie- 

 gated clays, sands) formations occur. The organic remains consist for the 

 most part of dinosaurs and plants. Lull, who has recently studied the former, 

 and Berry, who has been engaged in an investigation of the latter, are agreed 

 that they are of Lower Cretaceous age, so that the earlier questionable refer- 

 ence of the Patuxent and Arundel formations to the Jurassic is now abandoned. 

 Farther southward in North Carolina is the Cape Fear formation (arkosic 

 sands, clays), so called by Stephenson, which is evidently continuous with the 

 Patuxent formation, although the basal beds of the Coastal plain are trans- 

 gressed by later formations in southern Virginia and northern North Carolina. 

 No fossils have been found in the Cape Fear formation, but the strata are sim- 

 ilar lithologically to the Patuxent farther north and unlike the Arundel and 

 Patapsco. 



UPPER CRETACEOUS 



Upper Cretaceous deposits extend from New Jersey, where they are most ex- 

 tensively developed, northeastward along the New England coast and south- 

 ward through Delaware and Maryland to the Potomac valley. Strata of this 

 age have been penetrated in well borings in eastern Virginia, but do not appear 

 along the line of outcrop, being overlapped by Tertiary formations. In North 

 Carolina Upper Cretaceous deposits again appear, and cover a wide area to the 

 south of the Hatteras axis. 



