92 



PHYSIOGRAPHY AND GEOLOGY' OF THE COASTAL PLAIN PROVINCE. 



Among the forms which are restricted to the Aquia formation hut found 

 in hoih its memhers are : 



Turritella mortoHi Conrad 

 Tniritella hvineroso Conrad 

 Scahi virginianu Clark 

 Gibbtila gJanduJa (Conrad) 

 Panopea elongata Conrad 

 Meretrix ovata var. pyga ( Conrad ) 

 Dosiniopsis lenticttlaris (Rogers) 



Lucina aquiana Clark 



Venericardia planicosta var. rcgia Conrad 



CrassafeUites alaeformis Conrad 



Crassntellites aquimia Clark 



Ostrea compressirostra Say 



Leda cliftonensis Clark and Martin 



Trocliocyathus clarkeanus Vaughan 



Eupsammia ela borata ( Conrad ) 



The following species among others have l)een found only in the Piscata- 

 wav member : 



Trionyx virginiana Clark 

 Synechodus clarkii Eastman 

 Odontaspis elegans (Agassiz) 

 Phenacomya pefrosa (Conrad) 



Pholudomya marylandica Conrad 

 Lithophaga marylandica Clark and Mar- 

 tin 

 Ostrea compressirostra var. alepidota Dall 



The following species among others have been found only in the 

 Paspotansa member : 



Plcurotoma hnriifii Clark 



Plciirotoma putoinacriisis Clark and ^lar- 



tin 

 Caneellaria potonuicensis Clark and Mar- 

 tin 

 Miiru poiHonkeiisis Clark and ^Martin 

 Tiidicla marylandica Clark and ^Martin 

 Calyptraphorns jacksoni Clark 

 Aporrhais potomacensis Clark and Mar- 

 tin 



Diplodonta marlboroensis Clark and Mar- 

 tin 

 Crassatellites alta (Conrad) 

 Platidia marylandica Clark and Martin 

 Paracyathus murylandicus Vaughan 

 Bnlanophyllia desmophyllum Milne Ed- 

 wards and Haime. 



Areal distribution. — The Aquia formation outcrops along all the im- 

 portant streams and many of their tributaries in a narrow belt extending 

 from the Potomac Eiver to the James Eiver and passing through the counties 

 of Stafford, King George, Caroline, Hanover, Henrico, Chesterfield, and 

 Prince George with one isolated locality along the Nottoway Eiver in Sussex 

 County. The base of the formation rises above tide on Aquia Creek about 

 one-half mile east of the railroad crossing, about the same distance east of 

 the railroad on Potomac Creek, about 7 miles below Fredericksburg on the 

 Eappahannock, near the mouth of Massaponax Creek and at Deep Bottom 

 on the James Eiver. From these places the formation gradually rises 

 toward the west, appearing at higher and higher levels along the valley 

 slopes until it reaches to the height of the stream divides, where it is either 

 exposed or covered with a thin capping of Lafayette or Columbia materials. 

 The line of separation between the Aquia and ISTanjemoy has only been 

 determined in a few places because of the lack of suitable exposures. Along 



