220 W. M. Thornton, Jr. — A Feldspar Aggregate. 



After combining all the potash molecules with alumina and 

 silica to form orthoclase and likewise all the soda molecules to 

 form albite and all the lime molecules (except enough to satisfy 

 the phosphoric anhydride to form apatite) to form anorthite, 

 there is a little alumina in excess. This can be accounted for 

 by assuming the hornblende to contain some alumina, which 

 is probably the case, or by errors in the determinations. 



In general the methods of analysis employed were those in 

 use by chemists of the U. S. Geological Survey. In the 

 determination of the alkalis the purest reagents of Dr. T. 

 Schuchardt were used, and the filtrate from the first lime 

 precipitation was concentrated in a silver basin ; glass and 

 porcelain vessels were avoided where any error might arise 

 from their use. 



Virginia Geological Survey, 

 University of Virginia, January 16, 1911. 



