26 TRANSACTIONS OF THE [1888 



closely as it is possible for them to be placed. In the hardest 

 portions they are held together by an almost cherty matrix, but 

 in the less solidified parts, the shelly mass readily cracks apart 

 and yields the fossils in fairly good condition. Along that part 

 of the bank farthest from the bridge, the shells are densely 

 packed in the moderately loose greensand of the low terrace, and 

 here with a little effort they can be detached in bushels. Bivalves 

 constitute the greater part of the mass, and these are extensively 

 represented by casts, especially in cases where great pressure has 

 been exerted upon the shells. Occasionally a cast is found 

 distorted in a part of the rock where the action of violent com- 

 pression is perceptible in the surrounding elements. The most 

 abundant shell at Upper Marlboro is the Pectunculus stamineus 

 Con., although other genera and species are found in large 

 numbers. Cardita planicosta is common in the most indurated 

 part of the rock, and consequently is very difficult to extract. 

 The same may be said of Ostrea compressirostra Say, which is 

 here usually of small size, although a few loose valves of this 

 oyster may occasionally be dug out of the loose sand. 



Mr. Conrad visited this place as early as 1830, and gave a 

 short general description of it in the Journal of the Philadelphia 

 Academy of Natural Sciences. The latest writer upon the 

 Eocene formation of Maryland, Prof. Heilprin, reiterates the 

 statements of Mr. Conrad and Sir Charles Lyell relative to the 

 agreement of these beds with the Bognor rock of England 

 through some of their fossils, chief of which are this large 

 Ostrea and the Cardita planicosta. Besides the foregoing 

 species, this locality has yielded nearly all the kinds of Eocene 

 fossil shells thus far discovered in the State of Maryland. Both 

 TurriteUa Mortoni and Turritella humerosa have been taken by 

 myself from this locality, and I have likewise secured specimens 

 of Gucullea transversa, Nucidana protexta, Nucula parilis, Dione 

 ovata, Glycimeris elongata, CrassateUa alaeformis, and P/iolas 

 pjeirosa. 



The most conspicuous shell not yet detected in this locality 

 is the large and heavy Gucullea gigantea Conrad. Small 

 specimens of a Gucullea, more elongated than the G. gigantea, 

 and which appear to come between it and G. transversa 



