of the Middle A tlantie Coast Eoce 



ne. 



367 



No. 1. The thickness of the Eocene beneath 

 the basal strata of the Aquia Creek bluff, cannot 

 fall far short of 60 feet. Some exposures are 

 seen in the ravines to the west of the bluff, but. 

 no complete sequence of the beds has been 

 found. The almost entire absence of fossils 

 renders it impossible to say anything regarding 

 the faunal relations of the strata. The deposits 

 are typical green-sands, at times somewhat 

 argillaceous and with a basal pebble-bed over- 

 lying the Cretaceous at several points. 



No. 2. This bed is composed of dark uncon- 

 solidated green-sand packed chiefly with the 

 shells of Crassatella alceformis, Posiniopsis 

 lenticularis and Cytherea ovata. The bed is 

 about 12 feet in thickness at the upper end of 

 the Aquia Creek bluff, but gradually declines 

 in elevation until it passes below water level 

 about half way to Marlborough Pt. The same 

 bed appears at water level on the opposite side 

 of the Potomac river at Clifton Beach. 



No. 3. The green-sand marl composing this 

 bed is generally indurated so as to form a firm 

 band, 2 to 3 feet in thickness. The limestone 

 is highly glauconitic and of dark color, and is 

 filled with the shells, or more commonly the 

 casts of the same species as the previous bed, 

 together with Ostrea compressirostra and here 

 and there a specimen of Turritella mortoni. 



No. 4. This bed is a typical unconsolidated 

 green-sand containing large numbers of the 

 same forms as No. 3. It reaches about eight 

 feet in thickness. 



No. 5. This limestone bed is very persistent, 

 and forms a conspicuous ledge along the face 

 of the Aquia Creek bluff until it passes below 

 tide level near its eastern extremity. It is 

 commonly about two feet in thickness >nd is 

 packed with fossils among which the forms 

 mentioned below are conspicuous, in addition to 

 the species already mentioned as characteristic 

 for zones 2 to 5 which still remain the most com- 

 mon types, viz : Pholadomya marylandica, 

 Panopaza elongata, Tellina virginiana, Pholas 

 typetrosa, Fusus sp., Caricella sp., etc. 



No. 6. The dark characteristic green-sand 

 overlying the limestone ledge is packed with the 



17 



10 



15^ 



10 



