566 HENRY S. WASHINGTON 



ciardi's analyses show them to be very basic, with about 48—49 

 per cent, of silica. 



According to Klein they are gray, medium-grained rocks, 

 somewhat vesicular. Leucite, augite and olivine appear as 

 phenocrysts ; plagioclase is subordinate in amount both as 

 phenocrysts and in the groundmass. Klein remarks that as 

 olivine increases plagioclase decreases, though this relation has 

 apparently no influence on the structure. The groundmass is 

 made up largely of augite, with leucite, magnetite and plagio- 

 clase, occasionally biotite and haiiyne, and in one instance 

 nepheline. The presence of a glass base is not mentioned. 



Chemical composition. — A selection of what seems to be the 

 best and most typical of Ricciardi's analyses is given in the 

 table, together with the two of vom Rath. No. 3 was made by 

 myself in the Mineralogical-Petrographical .Laboratory of Yale 

 University, with the assistance of Professor L. V. Pirsson. I 

 gladly take this opportunity of expressing my sincere thanks to 

 him for his valuable assistance and advice. The general dis- 

 cussion of the analyses will be reserved for the final paper of 



the series. 



Henry S. Washington 



