154 THE SOILS OF PKINCE GEORGE^S COUNTY 



complex silicic acid is very weak as compared with the bases. 

 Although the mineral itself, perhaps, does not possess a large solu- 

 bility, in as far as it is soluble at all it will be dissociated and greatly 

 hydrolized.^ The result will be the formation of large quantities of 

 hydrates of potassium, calcium, and magnesium, which will in turn 

 be converted to the corresponding carbonates, or, more probably, 

 hydrogen carbonates, better known as bicarbonates, through the 

 absorption of and combination with the carbon dioxide contained in 

 considerable quantities in the atmosphere of all soils. 



The ferrous iron will also be largely converted into the hydrate 

 by the hydrolytic action of the water. But it will be further acted 

 upon by both the oxygen and carbon dioxide in the soil atmosphere, 

 so that the final product which it yields will be a more or less highly 

 carbonated ferric hydrate, and it is this material which forms the 

 cement of the pipes described above. As the analyses show, this 

 glauconitic material is unusually rich in potassium. 



Analyses are given in the following table of a greensand marl 

 obtained from an outcrop of the fresh material near Upper Marlboro, 

 in Marj'land, as well as of two soils and three subsoils. The method 

 of analysis chosen was the official one of the Association of Official 

 Agricultural Chemists — that is, the digestion in concentrated hydro- 

 chloric acid of specific gravity 1.115, This method was selected 

 principally because it would enable the results obtained on these 

 samples to be compared with those of other agricultural chemists, 

 and probably it furnishes as clear an idea as any other method would 

 of the agricultural values of the samples. 



It may be said in general that the results of this chemical exami- 

 nation show the chief value of the greensand marls of Maryland to 

 be due to the potash they contain, and which they slowly release as 

 they dissolve and break down in the process of weathering. To a 

 much less extent probably are they of value for their content of lime 

 and phosphoric acid. In this latter respect they do not compare 

 favorably with the similar marl deposits of New Jersey and some 

 other regions, which, while valuable for the potash they contain, are 

 more so on account of the very large content of phosphoric acid and 



iPor a general discussion of this subject the reader is referred to Bull. 17, 

 Division of Soils, U. S. Department of Agriculture, 1901. 



