60 THE EOCEXE DEPOSITS OF ilAKTLAXD 



To these may be temporarily added Zone 1, which, so far as known, is 

 devoid of determinable fossils, although indeterminate moUnscan casts 

 and plant remains have been found near the base of the zone. It is 

 possible that this zone should be made an independent stage, and it is 

 not improbable that it may represent a definitely lower Eocene horizon 

 than the more fossiliferous beds which overlie it, butjn the absence of 

 distinctive fossils it is impossible to definitely characterize it. It may 

 be regarded at present at least as the basal zone of the Aquia. 



The Aqtiia stage contains an extensive fauna. Among the forms that 

 are found in both substages are the following: 



Tkecachampsa sp. Payiopea elongata Conrad. 



Thecachampsa marylandica Clark. Jferetriz ovata var. pyga (Conrad). 



Cythere maryhrndka TJlrich. Lucina aquiana Cfark. 



Volutilithes up. Venericardia pTanicosta var. regia Conrad. 



Caricella pyruloides (Conrad). CrassaielJites aJaeformis Conrad. 



TurriteUa mortoni Conrad. CrassateU i.tes aquiana Clark. 



Turritella humerosa Conrad. Ostrea compressirostra Say 



Vermetus sp. Leda cliftmiensis Clark and Martin. 



Solarium sp. Trochocyathtis elarkeanus YsLUghan. 



ScciTa I'irgitiiana Clark. Eiipsaramia eUiborata (Conrad). 



Gibbula glandula (Conrad). Nodosaria comniuuis (d'Orbigny). 

 Gastrochaetia sp. 



Other species are restricted to one or the other of the substages and 

 are mentioned beyond. Additional to these are the forms previously 

 referred to as found in both divisions of the Pamunkey group. 



The Acjuia formation has been divided into two members which are 

 clearly separated by their contained faunas over considerable portions 

 of Maryland and Tirginia. They are known respectively as the Pis- 

 cataway and Paspotansa members or substages. 



THE PISCATAWAY MEMBER OK SUBSTAGE. 



The Piscataway member, so-called from Piscataway Creek which 

 empties into the Potomac river on the Maryland bank about ten miles 

 below the city of Washington, is characterized by greensands and green- 

 sand marls, the lower beds often quite argillaceous. Two well-marked 

 and rather persistent layers of indurated marl characterize the upper 

 beds in the Potomac region. The Piscataway member generally e.x- 

 ceeds 50 feet in thickness. 



