SECTIONS IN THE RAPPAHANNOCK RIVER VALLEY, 133 



On the right bank of the Eappahannock Eiver about 1 mile above the 

 month of Mount Creek there is a high cliff though the exposure of strata 

 is not good. Eocene greensand occurs at the base of the section while there 

 is a thickness of at least 50 feet of diatomaceous earth overlying it. 



I. Section, left bank Rappahannock River, one-half mile east of Wilmont 



Wharf. 



Feet 



Pleistocene Clay, sand and gravel 20 



Miocene. Calvert Diatomaceous clay, in places sandy especially 



near top and varying in the amount of dia- 

 toms. Dark green where unweathered but 

 lighter to almost pure white where weathered 94 

 Eocene. Nanjemoy Contact not well exposed. 



Dark green argillaceous glauconitic sand with 

 casts 6 



Total 120 



The purest diatomaceous earth observed is about 15 to 20 feet above the 

 base. The cliff is almost vertical and exposes an excellent section of the 

 Calvert formation. 



II. Section left hank of Rappahannock River, three-quarters of mile east 



of Wilmont Wharf. 



The section is similar to the one just given except that this is not so well 

 exposed throughout. The contact between the i!^anjemoy and Calvert 

 however, is well shown at a small waterfall near the western end of the 

 exposure. It occurs 2^^ feet above the water level. There is a sharp 

 change from the dark green glauconitic sand of the Nanjemoy to the light 

 olive green argillaceous sand which forms the base of the diatomaceous 

 clay. Along the contact there are occasional small pebbles ranging in size 

 up to iy2 inches in diameter, forming a basal conglomerate. In a thickness 

 of 3 feet the olive green sand grades up into the diatomaceous clay. The 

 base of the Miocene is evidently formed of the reworked Eocene material. 



III. Section left bank of Rappahannock River, two miles above the mouth 



of Elmwood Creek. 



Feet 



Pleistocene Yellow sand and gravel 10 



Miocene. Calvert Diatomaceous earth and clay originally dark 



or olive green, now various lighter shades to 

 white on surface. A very pure diatomaceous 

 earth layer occurs at an elevation of 85 feet 

 to 95 feet. The base is not well exposed but 

 a few hundred yards above at a small wharf 

 there is a pure diatomaceous earth layer 

 near the base 110 



Total 120 



