46 THE EOCENE DEPOSITS OF MAEYLAND 



with interstratified clays characterize the Earitan formation. The fos- 

 sils consist chiefly of the bones of dinosanrian reptiles and of leaf im- 

 pressions, the former confined to the Arundel formation, the latter pre- 

 dominating in the Patapsco and Earitan formations. The plants show 

 beyond a doubt the Cretaceous age of the two upper formations while 

 the reptiles have been regarded by high authority to be upper Jurassic. 



The Matawan formation is formed largely of fine sands and clays, 

 clearly stratified, and in the case of the clays often laminated. The 

 clays and sandy clays are generally dark, often black, in color. They 

 are commonly micaceous, and at time sparingly giauconitic. The very 

 homogeneous and persistent character of the beds is in marked contrast 

 to the deposits of the Potomac group which they overlie. The fossils 

 consist largely of marine Mollusca which indicate the upper Cretaceous 

 age of the deposits. 



The Monmouth formation consists chiefly of greensand deposits, 

 although the giauconitic element is not so pronounced or so persistent 

 south of the Chesapeake as in the more northern districts. The strata 

 are more arenaceous, and as a result the materials weather more readily, 

 showing generally in greater or less degree the characteristic reddish 

 color of the hydrated peroxide of iron. The common and characteristic 

 Gryphaea vesicularis, Exogyra costata, and Belemnitella americana are 

 widely found, with other typical forms. 



The Eancocas formation is also largely composed of greensands, gen- 

 erally more giauconitic than the Monmouth formation, although at 

 times somewhat argillaceous. The strata are much weathered where 

 exposed, and often appear as a firm red rock, the grains being cemented 

 by the iron oxide. The deposits have afforded Terebratula harlani, 

 Gryphaea h-yani, and other characteristic species of the New Jersey area. 



EOCENE. 



The Eocene is represented in the Middle Atlantic Slope by a group of 

 deposits stretching along the eastern margin of the Coastal Phiin and 

 overlying the Cretaceous formations unconformably. They will be 

 described in much detail in the following pages. 



The deposits consist largely of greensand marlp, which may, how- 



