BUI.LETIN lO 



30 3 



the huge boulders from the lower indurated layers lie scattered 

 along the beach. The same is also seen at Fort Washington, 

 Piscataway creek, Henson branch, Marlboro, Maryland, and at 

 other places. Where the glauconite has weathered the char- 

 acteristic bluish-green color is changed to a light gray or red- 

 ish-brown, which from the large amount of iron present is often 

 cemented into a ferruginous sandstone. This is particularly w^ell 

 illustrated in the bluffs along the Severn river. The land-de- 

 rived element which is present in addition to the argillaceous 

 material is chiefly quartz, together with some mica and some- 

 times these materials predominate forming beds of gray sands 

 or sandy clays. 



Prof. W. B. Clark mentions the occurrence of a coarse pebble 

 bed which has' been found in some localities at the base of the 

 formation. The following chemical analyses taken from Prof. 

 Clark's Report above mentioned serve well to show the com- 

 position of the greensand. 



Analyses of Marls. 



Woodstock, Evergreen, Aquia Creek, Winchester 



Va. Va. Va. IWd. 



H^O at 110° 3.58 3. II 0.76 1. 31 



Volatile at red heat 



less CO^ 2.84 2.60 ,21 6.27 



Al,0^&Fe,0,* 22.68 21.50 7.70 41-25 



CaO J. 66 2.50 36.78 None 



MgO ; 2.77 2.06 1.05 .76 



K,0 77 .61 .37 .39 



Nap 23 .31 .59 .42 



SiO^ 60.87 63.94 21.58 49.08 



CO, 3.17 3.53 29.79 .55 



PPj None None .09 .13 



98.57 IOC?. 16 98.92 100.16 



Silicious matter 73-48 75-85 25.36 52.30 



*A considerable Fe,0, in all samples. 



While the Eocene is more or less homogeneous throughout 

 its whole extent the Miocene shows marked variation in its 



