the Middle Atlwitic Slope. 127 



indications being that the river has here deepened its channel 

 several feet since 1839. 



The next exposures of the formation occur on the Appomat- 

 tox between Petersburg and its mouth at City Point ; the most 

 conspicuous beiug Point of Pocks (some four miles above the 

 mouth) where the larger part of the material is an arkose simi- 

 lar to that on Nottoway river, interspersed with well rounded 

 quartz aud quartzite pebbles and rounded or irregular masses 

 of plastic clay, interstratified with laminated clay beds, and the 

 whole so firmly lithified that the solid quartzite pebbles fracture 

 as readily as the matrix. The deposit here forms a prominent 

 bluff 50 or 60 feet high, the material of which has been largely 

 quarried as a building stone. 



On James river the formation is notably exposed between 

 Pichmond and Deep Bottom, a few miles above the mouth of 

 the Appomattox. Perhaps the most abundant constituent is 

 arkose, such as occurs on the Nottoway, generally friable but 

 sometimes lithified ; but the arkose beds are frequently interca- 

 lated with beds of massive or laminated clay and heterogeneous 

 sand or gravel, sometimes forming the greater part of the mass. 

 Where laminated, and especially in the lenticular bands inter- 

 calated between beds of arkose, the clay frequently contains 

 well preserved impressions of leaves ; and silicified wood is 

 common in the sandy and gravelly portions, as are lignitized 

 trunks and branches of trees in the beds of clay. One of the 

 most conspicuous elements in the deposits exposed on James 

 river is its large pebbles and bowlders, reaching three or four 

 feet in diameter, sometimes of Piedmont gneiss (which crops 

 out in the river channel within a few miles of Dutch Gap), 

 but more frequently of quartzite sometimes containing Scolithus 

 borings and casts of brachiopods identifying it with the axial 

 quartzites of the Blue Pidge. It is noteworthy that ~W. B. 

 Rogers recognized the materials of this formation in borings 

 from an artesian well at Fort Monroe at a depth of 835-907 

 feet.* 



Interesting exposures of the formation occur on the South 

 Anna river (where, as at Point of Rocks, it is in part a firmly 

 lithified arkose containing well rounded pebbles of quartz and 

 flakes and pellets of plastic clay) as well as on the Little river, 

 the North Anna, the Mat, the Taponi and its tributaries, on 

 Massaponax creek, and indeed in nearly every considerable 

 valley or deep ravine, and occasionally on the surface, between 

 the South Anna and the Rappahannock. It is generally over- 

 lain by the orange sands and clays of the Appomattox forma- 

 tion ; and in the neighborhood of Hanover Junction it reposes 

 unconformably upon the petrographically similar, but disturbed 



* Ibid., 733-5. 



