GREENSAND MARL. 247 



III. (No. 1322). Weathered diatomaceous eaith from 7th Street, near Richmond 

 Locomotive Works, S,ichmond. This, after burning, closely resembles 

 the diatomaneous earth near Layton along the Rappahannock River. It 

 seems to be vitrified at cone S, and at cone 8 is viscous. 



IV. (No. 1323). This sample was collected from the same locality as No. 1322, 

 but at greater depth below the surface. It is quite impure, and shows a 

 high air shrinkage. It burns red and becomes steel-hard at cone 05. It is 

 vitrified at cone 5, and nearly viscous at cone 8. 



V. (No. 1358). Diatomaceous earth along the Rappahannock River south of 

 Layton. This burns fairly dense at the higher cones, and gives a clean 

 color, but is quite porous at the lower cones. 



VI. (No. 1363). Diatomaceous earth from Wilmont. This burns to a very porous 

 body as is indicated by the absorption figures. It has a low air and fire 

 shrinkage. 



Though occurring in the Coastal Plain region in great abundance, the 

 deposits of diatomaceous earth are worked at present only to a very limited 

 extent. At Wilmont some of this material is mixed with Pleistocene clay 

 and used in the manufacture of brick. A few years ago it was quarried 

 and shipped from a point on the Rappahannock Eiver a short distance below 

 Wilmont but the plant has now been abandoned. According to the United 

 States Census office, the output of diatomaceous earth in Virginia in 1902 

 was limited to the production of two concerns. There has been no reported 

 production of diatomaceous earth in Virginia for several years. 



GREENSAND MARL. 



The Eocene and locally the Miocene deposits of A^irginia contain con- 

 siderable glauconite, a dark green mineral which is essentially a hydrous 

 silicate of iron and potash. The glauconite occurs in the form of small 

 grains, varying in amount from very nearly pure beds of that substance to 

 deposits in which the arenaceous and argillaceous elements predominate. 

 At certain places the shells of organisms are found commingled with the 

 glauconitic materials in such numbers as largely to make up the beds, pro- 

 ducing what is known as a greensand marl. Such a marl contains two of the 

 most important constituents to plant growth, potash and lime, while most 

 analyses show a small percentage of phosphate of lime even more beneficial 

 as a plant food. It is for these reasons that the greensand or glauconitic 

 marls have long been known to be of value as natural fertilizers. The marl 

 improves both the chemical and physical condition of the soil. It is very 

 lasting in its results, the effects being noticeable for many years, but its 

 bulkiness will probably always prevent it being extensively used in its 



