244 PHYSIOGRAPHY AXD GEOLOGY OF THE COASTAL PLAIN PROVINCE. 



I. Diatomaceous earth from the northern bank of the Rappahannock River at 

 Greenlaw's Wharf, King George County. F. W. Smither, analj'st. 



II. Diatomaceous earth from President's Hill, Richmond, Virginia. F. W. 



Smither, analyst. 



III. Diatomaceous earth from 7th Street, near Richmond Locomotive Works, 

 Richmond, Virginia. Eoff and Gibboney, analysts. 



IV. Diatomaceous earth from same locality as III. Eoff and Gibboney, analysts. 



V. Diatomaceous earth from the Rappahannock River south of Layton. Eoff 

 and Gibbone}^, analysts. 



VI. Diatomaceous earth from Wilmont on the Rappahannock River. Eoff and 

 Gibboney, analysts. 



It will be seen from examinatiori of these analyses that the earths show 

 much variation in their chemical composition. I, II, and III show low 

 silica, and the first two are described as being unusually pure, as indicated 

 by microscopic study. IV, V, and VI are quite siliceous and one of them 

 highly so. These are shown from microscopic study to be less pure than 

 I and II, and III and V are very impure. 



The diatomaceous deposits around Eichmond have long been known, and 

 are referred to in many publications. The beds outcrop in great thickness 

 in the embankments along the tracks at the Eichmond Locomotive Works, 

 and along the sides of the valley to the west. In general character the earth 

 is a silty porous clay, which breaks out in irregular lumps. In places it is 

 traversed by vertical fissures which are filled with limonite. Analyses II, 

 III, and IV in the table above are of diatomaceous earth occurring around 

 Eichmond. 



There are long exposures of diatomaceous earth along the Eappahannock 

 Eiver, especially in the vicinity of Layton and Wilmont. The diatomaceous 

 earth beds have a thickness of about 50 feet and stand out in bold almost 

 vertical cliffs, which when viewed at a distance present an appearance almost 

 as white as chalk. These cliffs stand out prominently in the sunlight and 

 can be seen for a long distance. This earth is apparently purer and lighter 

 than much of that around Eichmond, and like the latter it passes in places 

 into clay. Analyses I, V, and VI in the table above are of diatomaceous 

 earth occurring at Greenlaw's Wharf, King George County, and near 

 Layton and Wilmont, Essex County, on the Eappahannock Eiver. Other 

 good exposures of the earth are at Carter's Wharf on the Eappahannock 

 Eiver, and along Shockoe Creek in the eastern part of Eichmond with an 

 indicated thickness of about 30 feet. 



