XXViii INTEODUCTION 



frequently arkosic, with gravel at certain points where the shore accu- 

 mulations are still preserved. The deposits of the Patuxent formation 

 are highly arkosic, the sands and clays showing both a vertical and a 

 horizontal gradation into one another. The sand layers are seldom widely 

 extended, being generally lenticular masses which rapidly diminish in 

 thickness from their centers. Dark-colored clays abound in the Arun- 

 del formation and have yielded large amounts of nodular carbonate of 

 iron. Highly-colored and variegated clays largely make up the Patap- 

 sco formation. Thick-bedded and widely extended white sands with 

 interstratified clays characterize the Earitan formation. The fossils 

 consist chiefly of the bones of Dinosaurian reptiles and of leaf impres- 

 sions, the former confined to the Arundel formation, the latter predom- 

 inating 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 case of the clays often laminated. The clays 

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

 commonly micaceous and at times sparingly glauconitic. 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 glauconitic 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 

 Gryphcea vesicularis, Exogyra costata, and Belemnitella americana are 

 found, especially in the basal beds. 



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

 erally more glauconitic 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 Terehratula harlani, 

 Gryphcea hryani and other characteristic species of the New Jersey area. 



