66 PHYSIOGRAPHY AND GEOLOGY OF THE COASTAL PLAIN PROVINCE. 



mont Plateau. The outcrop is more or less continuous from Washington to 

 the Eappahannock Eiver at Fredericksburg. South of Fredericksburg 

 exposures are seen only along the banks of the larger streams. In the vicinity 

 of Doswell it outcrops along the North Anna Eiver for a distance of several 

 miles above the confluence with the South Anna Eiver which unites with 

 the former to form the Pamunkey. In the vicinity of Eichmond the 

 Patuxent is exposed almost continuously along the banks of the James 

 Eiver from the State capitol to Jones Neck a few miles above Bermuda 

 Hundred, exhibiting a number of most excellent exposures, notably at 

 Drewrys and Chaffins bluffs and in the vicinity of Dutch Gap. In the 

 Petersburg region the Patuxent outcrops along the Appomattox Eiver at 

 intervals from that town to within a short distance of its junction with the 

 James Eiver at City Point. Numerous exposures are to be observed, notably 

 at Point of Eocks. The most southerly exposures of the Patuxent in Vir- 

 ginia are found to a limited extent in the valley of the Nottoway Eiver in 

 western Sussex County, although these have not been seen by the writer. 

 No other river in southern Virginia has succeeded in cutting a channel to 

 the Potomac surface, although it may be noted that unmistakably reworked 

 Patuxent materials are abundant in the Pleistocene in the vicinity of 

 Emporia. South of the Virginia line the Patuxent formation extends 

 across North Carolina, broadening out to a remarkable extent in the upper 

 Cape Fear basin around Fayetteville. 



The Arundel Formation. 



(not recognized in VIRGINIA.) 



The Patuxent formation is succeeded in the Maryland area by a series 

 of stratified clay beds, fine in texture and brown in color, carrying a large 

 amount of carbonaceous matter and considerable deposits of iron ore which 

 were used extensively in colonial days. These beds, long known as the 

 "iron ore clays," contain a varied flora scarcely distinguishable from that of 

 the Patuxent formation, and a considerable, chiefly dinosaurian, fauna 

 which finds its counterpart in the Morrison beds of the "West and the 

 Wealden of Europe. 



The Arundel deposits are thought to represent discontinuous swamp 

 and lagoon accumulations in warped valleys of post-Patuxent time and are 

 therefore unconformable upon the older beds. They owe their iron to the 

 fact that their sediments were largely derived from the decay of gabbro 

 and other iron-rich crystallines lying immediately to the westward of the 



