PETROGRAPHY OF SOME NORTH CAROLINA SOILS AND 

 ITS RELATION TO THEIR FERTILIZER REQUIREMENTS 



By J. K. Plummer, 

 Soil Chemist, Division of Agronomy, North Carolina Agricultural Experiment Station 



INTRODUCTION 



In connection with the detail study of the soils of North Carolina, the 

 writer has had occasion to make many mineralogical analyses of the 

 existing soil types as defined by the United States Bureau of Soils. These 

 examinations have included all types of any prominence thus far en- 

 countered in the survey and give some rather interesting data as to the 

 formation and character of these soils which may be of more than local 

 interest. 



The available data showing the mineral composition of soils are 

 meager. The scope of those found is so broad that definite conclusions 

 can hardly be drawn as to the relationships which exist between the 

 mineral component and the character of soils. The behavior of the 

 various soil-forming minerals toward the forces of weathering will have 

 to be known before the soil investigator will be able to solve many of the 

 complex problems confronting him. 



The methods used in these analyses are essentially those compiled 

 by McCaughey and Frye.^ Unfortunately, one serious criticism may be 

 made regarding these methods — i. e., the defiance of members of the clay 

 group against identification. It is quite possible that this group plays 

 the most important r61e in the various soil phenomena of all the sepa- 

 rates which compose the soil. Yet it would seem that since the clay 

 owes its origin to the coarser particles, some definite knowledge of 

 the composition of the latter would be imperative. 



SOILS OF NORTH CAROLINA 



The soils of North Carolina are quite heterogenous and furnish well- 

 defined examples for a discussion of the petrography of soils. The 

 State is divided into three provinces, determined largely by the physio- 

 graphic provinces used in any study of physical geography. There are 

 the old Appalachian, locally known as the Mountain section. Piedmont 

 Plateau, and Atlantic Coastal Plain. As will be shown later, wide varia- 

 tions in the mineralogical composition of the soils of these provinces are 

 encountered. 



Practically all of the soils of the mountains are of residual origin and 

 are derived from igneous and metamorphic rocks, mainly gneiss, schists, 



1 McCaughey, W. J., and Fry, W. H. The microscopic determination of soil-forming minerals. U. S. 

 Dept. Agr. Bur. Soils Bui. 91, 100 p., 12 fig., 12 tab. 1913. Bibliography, p. 99-100. 



Journal of Agricultural Research, Vol. V, No. 13 



Dept. of Agriculture, Washington, D. C. Dec. 27, 1915 



bp (569) N. C.-2 



