248 PHYSIOGRAPHY AND GEOLOGY OF THE COASTAL PLAIN PROVINCE. 



natural condition except locally. From 60 to 100 bushels per acre should 

 be used on sandy soils and from 160 to 200 bushels on clay soils. 



Greensand deposits of Upper Cretaceous age have been worked for more 

 than 100 years in New Jersey and almost invariably the users report 

 increased soil fertility. Similar deposits of Tertiary age have been worked 

 in Delaware, Maryland, and Virginia but to a less extent. To obtain 

 the best results the marl should be dug and allowed to weather for a few 

 months in order to permit all the firmer masses to disintegrate, after 

 which it is spread over the surface of the ground in a thin layer. 



Besides serving as a natural fertilizer, greensand marl is now fre- 

 quently used as a base in the manufacture of artificial fertilizers. For 

 this purpose the greensand is dried, pulverized and then shipped to the 

 fertilizer plants. Most of the greensand marl now dug in New Jersey 

 and Virginia is being used in this way. 



The distribution of greensand marl in Virginia is almost coextensive 

 with the distribution of the Aquia and Nanjemoy formations, as both 

 of these contain a great deal of glauconitic sand. The region along the 

 Pamunkey Eiver is underlain by valuable deposits and more has been 

 dug there than at any other locality in the State. Similar material outcrops 

 along the Potomac and the Rappahannock rivers and their tributaries in 

 Stafford, King George, and Caroline counties and along the James River 

 and its tributaries in Henrico, Charles City, and Prince George counties. 

 Extensive beds of greensand marl occur in portions of James City, York, 

 Hanover, Chesterfield, Prince William, and Spottsylvania counties. The 

 beds vary greatly in depth and in the amount of potash and phosphoric 

 acid contained. Potash varies according to the proportion of the mineral 

 glauconite present, ranging usually from one per cent in the very impure 

 greensands to 8 and 10 per cent in the purer greensands. Shells are usually 

 present in the deposits and supply lime in addition to potash and phos- 

 phoric acid. 



Greensand marls have been dug at a number of places on the James 

 and Pamunkey rivers. The most important place for the production 

 of marl within recent years is on the James River in Prince George County 

 a few rail°s below City Point. The marl was there dug, dried and shipped. 

 Some Miocene shell marl was also ground up with the greensand marl. 



The following analyses, made of greensand marls collected from 

 Hanover, Suffolk, and Prince George counties, Virginia, and Aquia Creek, 

 Stafford County, Virginia, serve to show their composition: 



