Dec. 27, 1915 
Petrography of Some North Carolina Soils 
58i 
combe field the content of phosphoric acid is somewhat less than that of 
the Cecil clay loam at the Iredell farm, yet in the latter soil phosphorus is 
the limiting element; but this is not the case in the former, owing doubt¬ 
less to the way this constituent is held in the two soils. The supply of 
phosphorus must be stored in the organic form. There is practically no 
apatite in this Norfolk soil, while it is readily encountered in the residual 
soils of the Piedmont Plateau, occurring both free and included in quartz 
and other minerals. 
CONCLUSIONS 
The results of this and other work on the subject indicate that the 
following conclusions can be drawn, some of which are undoubtedly 
applicable to other than North Carolina conditions. 
Wide variations in mineralogical composition are found between the 
soils of the Appalachian Mountains, Piedmont Plateau, and Atlantic 
Coastal Plain. There is unquestionably a greater supply of minerals 
which carry the inorganic plant-food constituents in the Mountain soils 
than are found in either the Piedmont Plateau or the Coastal Plain. 
Though many of the former soils are derived from the same rocks as 
those of the Piedmont province, the forces of erosion among those of the 
mountains cause them to contain minerals more nearly the same as the 
parent rocks than are found elsewhere. 
Definite information is required on the behavior of the various soil¬ 
forming minerals to the forces of weathering before positive conclusions 
can be drawn on the availability of the plant food carried by the different 
minerals. 
The field results with the cotton plant indicate that there are some 
relationships existing between the mineral component of the soil and the 
requirements of this plant for the three inorganic fertilizer constituents, 
phosphoric acid, potash, and lime. 
