MAKYLA]?^D GEOLOGICAL SURVEY 



153 



surface is gently rolling or nearly flat and lies at an elevation of 

 from 80 to 160 feet above sea level. The original forest growth has 

 been removed over this soil area, and with a very few exceptions the 

 land is under a high state of cultivation. The usual staple crops of 

 corn, wheat, and tobacco are cultivated upon this soil type. Wheat 

 produces about 10 bushels and corn from 25 to 35 bushels per acre, 

 while the tobacco raised is of good quality, yielding from 700 to over 

 1,000 pounds per acre. 



The Collington sand is derived through the natural process of 

 weathering from the Aquia formation of the Eocene period. The 

 material constituting this formation consists of the mineral glau- 

 conite, a complex silicate of the bases potassium, calcium, mag- 

 nesium, and ferrous iron, containing also some phosphoric acid. It 

 is mixed with medium to coarse grained quartz sand. This mate- 

 rial still remains imconsolidated, except for a narrow band of silice- 

 ous rock only a few feet in thickness, which has very little influence 

 upon the soil of the region. 



The Collington sandy loam as a soil type has been directly derived 

 from the outcroppings of this greensand. Upon exposure to the 

 weather the dark-green glauconitic material is affected chemically by 

 the action of rain water and the impurities which it carries in solu- 

 tion. The quartz grains contained in the greensand are only slightly 

 dissolved during the chemical reactions which follow. On the other 

 hand the glauconite, which is a very complex and unstable silicate, is 

 altered in its chemical composition. Salts of potassium, magnesium, 

 calcium, and iron are formed, and these, being soluble to different 

 degrees, are unequally leached away by the circulation of the soil 

 waters. The iron salts, in particular, frequently accumulate in the 

 form of pipes, tubes, and irregular concretions of hydrated carbonate 

 of iron, binding together grains of quartz sand. These pipes are fre- 

 quently filled wdth unweathered or partly weathered glauconite. 



Glauconite, as is the case with the greater number of minerals, is 

 a salt, but a very complex one, containing, as stated above, potassium, 

 ferrous iron, calcium, and magnesium as bases, the bivalent elements 

 replacing each other in somewhat indeterminate quantities. The 



