MARYLAND GEOLOGICAL SURVEY 189 



part of the last century, yet their importance in the enrichment of the 

 soil has never been generally recognized. At present their use in Mary- 

 land has been almost entirely discontinued although the deposits are 

 practically inexhaustible. 



The Eocene marls are glauconitic in character and constitute the 

 entire thickness of the Eocene deposits which outcrop in the north- 

 western corner of the county along Lyons Creek and the Patuxent River. 

 They consist of quartz sand with an admixture of many grains of glau- 

 conite, a soft green mineral which is essentially a hydrous silicate of 

 iron and potassium. On account of the glauconite, the marls arc green 

 in color and are commonly known as " greensand marls." They are also 

 rich in calcium carbonate, derived from the shells which are abundant in 

 the deposits, and chemical analyses usually show the presence of small 

 amounts of mineral phosphates. The marls thus contain three important 

 plant foods — potash, lime, and phosphates. Altogether these form only 

 a small percentage of the entire content of the marl, yet, wherever the 

 marls can be obtained at low cost, they furnish economical means for 

 increasing soil fertility. In New Jersey, Delaware, and the Eastern 

 Shore of Maryland where similar marls are found in the Cretaceous 

 deposits, they have been extensively worked and almost everywhere re- 

 garded as valuable fertilizers, it being claimed that the beneficial effect 

 of the glauconitic marl is much more lasting than that obtained by the 

 use of artificial fertilizers. The method of application is to scatter 

 thinly over the surface during the winter months and plow under the 

 following spring. In Calvert County, because of the small area where 

 these marls appear at the surface, they can never be of any great value 

 to the entire county but might be profitably used in the vicinity of their 

 outcrop. 



The shell marls of the Miocene also possess valuable fertilizing proper- 

 ties for soils deficient in lime. The shell beds outcrop almost continu- 

 ously in the cliffs of the Bay shore and are encountered along the valleys 

 of the streams tributary to Chesapeake Bay and the Patuxent River 

 throughout the greater portion of the county. In places the shells are 



