INTERMEDIATE CHARACTER OP APPALACHIAN GRANITES 



37 



the western granites. Similarly small differences in the averages of the 

 different kinds of feldspar molecules (orthoclase, albite, anorthite, and total 

 plagioclase) for the tiiree sections are indicated. Though the difference is 

 very slight, the Southern granites show the smallest average for orthoclase 

 and the largest for total plagioclase of the three sections. For this reason 

 the average ratio of orthoclase to plagioclase is propoitionately larger for 

 the Southern granites than for those of New England and the western 

 United States. These relations between the feldspar of the three sections 

 are represented diagrammatically in figure 3. 



Average of 40 

 Southern y/e?/7//es 



Average of 9 

 New Jersey fren/>es 



Average of 2t 

 f^w&ig^riti graniVes 



Average of 30 

 fVestern gran if es 



Figure 3. — ^Diagram illustrating feldspar composition of granites in the United 

 States by sections. 



Southe-ni granites. 



'Average of 40 analyses distributed as follows: Maryland 9, Virginia 7, North 

 Carolina 7, South Carolina 8, and Georgia 9. 



