Alt. II.] Watson, Aplitc, Pegmatite, and Towmalme. 19 



constituents. A striking feature of the analyses is the low per- 

 centage of lime with practically no magnesia, and increased 



I. Aplite, Stone Mountain, Georgia. Watson, analyst. 



II. Stone Mountain granite inclosing aplite. Packard, analyst, 

 la. Molecular ratios of I. 



Ila. Molecular ratios of II. 



soda, which equals in amount the potash, indicating the pre- 

 dominance of the albite molecule over that of theanorthite, and 

 in case of the aplite the nearly entire absence of magnesia 

 harmonizes with the absence of a ferro-magnesian accessory. 

 Calculating all the lime as anorthite, all the soda as albite, and 

 all the potash as orthoclase or microcline, the mineral composi- 

 tion of the aplite and granite becomes : 



' Analysis made in the chemical laboratory of Denison University. 

 * All iron determined as ferric oxide. 



