62 TRANSACTIONS OF THE [1889 



Immediately above this, the compact black marl of the Eocene 

 forms the steep walls of the ravine, and keeps on stage after 

 stage until it terminates in the more loamy greensand-marl 

 which rises to within five or six feet of the surface of the high- 

 land. At the first exposure above the Cretaceous, the Eocene 

 black marl displays a thickness of about five feet above the bed 

 of the stream, and holds specimens of Ostrea eom'presdrostra, its 

 top is then eroded, and we ascend a few feet before its continu- 

 ation appears. It is now much thicker, and increases as it 

 ascends, until the thickest part reaches to a height of about ten 

 to twelve feet. This is the member in which the Latiarca 

 gigantea is found, accompanied by the Ostrea compressirostra, 

 and casts of Dosiniopsis meekii. Another stage has been cut 

 above this, but there is after this no break in the continuity of 

 the bed as it rises towards the summit. It is simply cut into 

 uneven terraces by the aqueous forces which have eroded the 

 brow of the ridge. From this point up, the fossil shells are 

 arranged in separate horizontal layers, a few inches or feet in 

 thickness. These consist of one series of remotely placed speci- 

 mens of the Dosiniopsis, next a similar bed of the Ostrea 

 followed above by a close deposit of Turritella mortoni, and this 

 in turn by small specimens of the same Ostrea until near the 

 top of the black marl bed. The few feet of greenish marl which 

 rests above this, and finishes the Eocene at this locality, has 

 hitherto yielded no fossils. It is of the type common above the 

 shell-r.ock near Upper Marlboro and in many parts of Anne 

 Arundel county, but it seems everywhere to be an almost barren 

 member of the series of Eocene deposits. 



This ravine is a typical one in most of its features, and it has 

 the great advantage of displaying its exposures in undisturbed 

 order. It has yielded fewer species of fossils than most of the 

 other ravines in this section of country, but it is remarkably 

 clean in most of its divisions, and exhibits the fossils in perfect 

 form, although difficult to extract because of their friable 

 condition. 



The whole thickness of the deposit through this part of the 

 ridge exceeds sixty feet, and it is here overlaid by the loam and 

 gravel presumed to be of Quaternary origin. Several adjacent 



