DIATOMACEOUS EAKTH. 



343 



each year in the manufacture of brick, and in railway, highway, and side- 

 walk construction, etc., of which no record of the quantity used is kept and 

 no returns are made to the office of the State Survey. Much the largest 

 proportion of sand used in the State, for which returns are made, is for 

 building and molding. 



DIATOMACEOUS EARTH. 



Diatomaceous earth, known in the trade under the name of "silica," 

 "infusorial earth," or "tripoli," is composed of the minute shells or tests of 

 microscopic plants known as diatoms, and is widely distributed in the 

 Calvert formation. It was first reported from the vicinity of Eichmond, 

 Virginia, and for that reason received the name of "Eichmond earth," under 

 which term it is sometimes referred to in the literature. Because of its 

 occurrence at Bermuda Hundred on the James Eiver, it has been called 

 "Bermuda earth." 



The first bed of diatomaceous earth of any extent discovered in this 

 country was in the Eichmond area. It is known as the Eichmond bed, which 

 extends from Herring Bay on the Chesapeake, Maryland, to Petersburg, 

 Virginia, and probably beyond. It is not less than 30 feet in thickness in 

 places, though very impure at times, grading frequently into layers of clay. 

 It is of Miocene (Calvert) age, light brown and red to almost pure white 

 in color, and is exposed along the numerous streams close to their crossings 

 from the crystalline rocks on to the sediments of the Coastal Plain. 



Specimens of the diatomaceous earth collected from various points in 

 the Virginia Coastal Plain region gave the following results on analysis : 



Analyses of Virginia Diatomaceous Earth. 



aSmither, F. W. Analyses of Infusorial Earth. Amer. Chem. Jour., 1897, 

 Vol. XIX, pp. 235-23G. 



6Ries, Heinrich. A Preliminary Report on a Part of the Clays of Virginia. 

 Bull. No. II, Geological Series, Virginia Department of Agriculture and Immi- 

 gration and Virginia Polytechnic Institute, 1906, p. 143. 



