6^ THE EOCEXE DEPOSITS OF MARYLAND 



Zone 12. — A greenisli-gray argillaceous sand, containing few tin- 

 weatliered grains of greensand. Xo fossils have been found in it. The 

 bed is 8 or 9 feet thick. 



Zone 13. — This bed consists of a light-gray glanconitic sand, generally 

 somewhat weathered. It is crowded with shells of Venericardia potapa- 

 coensis, and also contains TornateJlaea hella, Cadiilus ahruptus, etc. 



It is 3 feet in thickness. 



Zone IJf. — Overlying the Venericardia layer is a bed of greenish-gray 

 argillaceous sand, some 4 to 6 feet in thickness, that contains a great 

 number of bands filled with gypsum crystals. ISTo fossils were observed. 



Zone 15. — This bed consists of greenish-gray argillaceous sand, in 

 which the glauconite grains have often been extensively weathered. 

 The bed has a thickness of 12 to 25 feet. 



At various localities in Charles county, notably about Port Tobacco 

 and at the headwaters of Xanjemoy Creek, this zone contains a fauna 

 that is Cjuite distinct from either the Ac{uia or Woodstock faunas. It 

 is an unweathered greensand, and very argillaceous at these localities. 

 The top of the bed is marked by a well-developed layer of concretions. 

 This layer passes below water-level about 2^ miles above the mouth of 

 Popes Creek, and is to be seen about sis feet above the base of the bluff 

 at TVoodstock. > 



THE WOODSTOCK MEMBER OR SUBSTAGE. 



The Woodstock member, so-called from Woodstock, which is an old 

 estate situated a short distance above Mathias Point on the Virginia 

 bank of the Potomac, is characterized by fine, homogeneous greensands 

 and greensand marls, that are less argillaceous than the underlying 

 Potapaco beds. The member has a thickness of 50 to 60 feet. 



The Woodstock substage embraces Zones 16 and 17 and contains the 



following species in addition to those previously mentioned as ranging 



throughout the Xanjemoy, viz.: 



Carcharodon auriculatKs (Blainville). (.«') Leda parilis Conrad var. 



Galeocerdo latidens Agassiz. Spii'oplecta clarki Bagg. 



Olivula sp. Nodomria affinis (d'Orbigny\ 



LevifiiHus trabeatns (?) Conrad. Cristellaria radiata Borneraan. 



Levifusus trabeatns (?) luir. Pohjmorphina austriaca (d'Orbigny). 



rijrnla penita Conrad, var. Pohjmorphina eleqanthHima Parker & Jones. 



Pjrnla sp. Pot ijniorphina pracloiiga Terquem. 



