52 the eocexe deposits of makylaxd 



Gexeeal Chaeactee of the Deposits, 

 compositiox. 



The Eocene deposits of the Middle Atlantic Slope are typically glau- 

 conitic, and are found in their nnweathered state either as dark gray or 

 green sands or clays. The glauconite varies in amount from very nearly 

 pure beds of that substance to deposits in Avhich the arenaceous and 

 argillaceous elements predominate, although the strata are generally 

 very homogeneous through considerable thicknesses. At certain hori- 

 zons the shells of organisms are found commingled with the giauconitic 

 materials in such numbers as largely to make up the beds, producing 

 what is known as a greensand marl. These beds are at times so indu- 

 rated as to form true limestone ledges. This latter phase is seen typi- 

 cally developed both at Fort "Washington and Aquia Creek, interstrati- 

 fied with the unconsolidated greensand layers. 



When the glauconite is weathered the deposits lose their character- 

 istic gTay or green color and generally become lighter gray with reddish 

 or reddish-brown streaks or bands, or may be entirely of the latter color. 

 This change to red beds particularly characterizes the Eocene deposits 

 of the northern portion of the area, from the Patuxent valley to the 

 Delaware line. Throughout much of this territory the beds are coarse 

 sands and become predominently so toward the northeast. This type of 

 material is well seen on Mount Misery on the north bank of the Severn 

 river and at various points on the Chester river, where it is often ce- 

 mented into a ferruginous sandstone. In the less completely weathered 

 portions of the formation farther south the change is indicated by the 

 mottled yellow and brown appearance of the more superficial beds, many 

 of the giauconitic grains still showing their green color when crushed. 

 Thin iron crusts at times appear in strata of this character. 



It is noteworthy that in the northern portion of the area the cement- 

 ing medium of the indurated beds is either ferruginous or siliceous 

 while in the southern portion it is chiefly calcareous. 



When the glauconite is largely or, more rarely, entirely absent in the 

 original materials, the deposits consist of black or gray sands or clays, 

 the latter at times micaceous, and in a few instances carbonaceous. 



A microscopical examination of several selected specimens from dif- 



