552 



HENRY S. WASHINGTON 



brown, irregular in outline and show without exception great 

 "magmatic" alteration. The product is largely magnetite with 

 little augite, and penetrates deeply and irregularly into the crys- 

 tal. Magnetite is quite abundant, both in the groundmass and 

 as phenocrystic grains. The groundmass is t3^pically trachytic, 

 and consists essentially of a holocrystalline cement of soda 

 orthoclase flakes and laths, which latter are more abundant in 

 the gray vulsinite than in the brown streaks. There is little evi- 

 dence of flow structure. With these are numerous grains of 

 yellow or greenish augite, magnetite grains and some apatite 

 needles and grains of titanite. There are also seen some small 

 crystals of a peculiar brown hornblende, which will be described 

 at length later. No glass is present and the rock does not gel- 

 atinize with acids. 



Here and there one sees coarse-grained, holocr3^stalline clus- 

 ters of large augite, plagioclase, orthoclase and magnetite grains^ 

 which are probably segregations, as Klein suggests. The augite 

 is generally bright golden-yellow, but a few pale green diopside 

 grains are to be noticed. It is xenomorphic towards the feld- 

 spars, filling the interstices between them. The feldspars con- 

 tain large dusty apatite crystals. 



Three analyses of this rock are inserted here. 



1. Vulsinite, Nassini's Quarry, Bolsena, VOM Rath, op. cit., 291. 



2. " Bolsena, Ricciardi anal. Klein, op. cit., 8. 



3. " Bolsena (665), Washington anal. 



