APPOMATTOX RIVER SECTIONS. 79 



While the lithology of the Potomac portion of this exposure is not to 

 be differentiated from that of the preceding sections the fossils indicate 

 that it represents a remnant of the Patapsco formation, the most southerly 

 one known, as well as the only recognizable exposure of this age on the 

 James Eiver, marking the point where the Potomac dissappears beneath 

 tide. 



APPOMATTOX RIVER SECTIONS." 



N"o satisfactory exposures of Potomac strata occur at Petersburg although 

 low exposures of Patuxent arkosic sand are to be seen in various road cut- 

 tings in the vicinity of the town. The river banks are low for some miles 

 below, the only notable Potomac section on the river being that at Point of 

 Eocks, although the Patuxent is exposed more or less along the right bank 

 for some 31/2 miles above the Point. The banks are much slipped and poorly 

 exposed and furnish nothing worthy of comment except occasional traces 

 of plant fossils, none of which are complete enough for accurate identifi- 

 cation. 



At Point of Eocks, which is on the left bank about 4 miles above City 

 Point, the only good section on the river shows the following details : 



I. Section at Point of Bocks. 



Feet 

 Pleistocene Argillaceous sand with gravel bed containing 



cobbles along the base 5-12 



Lower Cretaceous. Patuxent Lenticularly cross-bedded coarse arkosic sand 



with scattered cobbles in places, firmly and 

 extensively indurated 75-80 



Total 92 



The minor details of this section are very variable, no two points along 

 the bluff showing exactly the same succession. 



Below Point of Eocks the left bank of the Appomattox is low and shows 

 no exposures while along the right bank for a distance of about two miles 

 occasional poor exposures of Potomac materials rise from 10 to 20 feet above 

 tide and are overlain with Eocene or Pleistocene. One of these about 

 one and a fourth miles below Point of Bocks shows the following; section : 



"The writer had the benefit of Mr. Arthur Bibbins notes of the Appomattox 

 River section. 



