132 PHYSIOGRAPHY AND GEOLOGY OF THE COASTAL PLAIN PROVINCE. 



SECTIONS ALONG THE TRIBUTARY STREAMS OF THE "NORTHERN NECK." 



The belt of land lying between the Potomac and Rappahannock river 

 estuaries and commonly known as the "jSTorthern Neck," topographically 

 consists of a flat dissected upland about 150 to 200 feet in elevation, with 

 narrow terraces separating the central divide from the rivers. In most places 

 the main streams have cut low cliffs in the lower terraces but in a few places 

 the rivers have cut back to the main divide and high cliffs result. The 

 Nomini Cliffs on the Potomac Eiver have already been described. On the 

 Eappahannock, similar cliffs exposing the Calvert deposits occur at Wilmont 

 and near Carter's Wharf. 



Along the small streams tributary to the Potomac and Rappahannock 

 rivers in King George, Westmoreland, and Richmond counties, the Calvert 

 formation is exposed in hundreds of places. In general the slopes of the 

 hills are steep and the Calvert is exposed continuously along the sides of the 

 valley. The following sections are characteristic. 



Just below mill dam about I14 miles west of Montross there is an 

 exposure of Calvert argillaceous sand which grades into arenaceous clay. 

 Where unweathered it is bluish-drab; where weathered a light gray. The 

 exposed thickness is about 85 feet. Similar Miocene material is exposed 

 in stream cuttings at several points between Montross and Ethel. 



On road between Ethel and Farmers Fork, about one-half mile from 

 Ethel, the road crosses a stream where there is a mill. Just below the dam 

 there is a good exposure of Miocene blue sand about 10 feet in thickness. 

 Upper part is weathered and grayish in color. Above this and poorly 

 exposed in the creek bluff there is a thickness of about 40 feet of Miocene 

 drab clay above which is Pleistocene ferruginous sand containing a few 

 pebble lenses and iron stone layers. 



SECTIONS IN THE RAPPAHANNOCK RIVER VALLEY. 



The Calvert formation extends along the Rappahannock River for a 

 considerable distance and is exposed in many places. In most places the 

 exposures consist of only a few feet of diatomaceous earth or blue sandy 

 clay outcropping at the base of the low banks which the river has cut in the 

 lower Pleistocene terrace. In certain places, however, the river has cut into 

 the liigher lying terrace and high cliffs result in which are excellent 

 exposures of Calvert strata. In general the sections display little variety 

 of material. 



