234 Van Hise — Enlargements of Hornblende Fragments. 



between crossed nicols the lighter colored, most irregularly 

 outlined exterior parts are optically continuous with the inte- 

 riors of the grains. Quite frequently the individuals of horn- 

 blende are twinned, and in this case the added portions are 

 also twinned in a corresponding manner, the twinning bands 

 cutting directly across both the cores and the new bordering mate- 

 rial. 



The proof that these are really enlargements of hornblende 

 fragments is, then, much the same as that hitherto advanced 



[■rt-%. 



W* 



One millimeter. 



of the enlargements of quartz and feldspar. The more impor- 

 tant of these are indicated by the figures in the accompanying- 

 plate. 



Figures 1 and 2 are enlarged rounded grains of hornblende. 

 The curved lines represent the broad lines of division between 

 the old and new hornblende. This line is not an unbroken, 

 sharply continuous one, but is built up of small gas cavities 

 and particles of ferrite. With a low power the ferrites and 

 cavities make an apparently unbroken line, but with a higher 

 power their true character is plain. The sharply serrate out- 



