E. 8. Dana — Petrography of the Sandwich Islands. 443 



clase, and titanic, or magnetic iron or both, prominent, but with 

 little or no chrysolite. Their most interesting feature is the 

 form taken by the augite, which is only exceptionally devel- 

 oped as an idiomorphic constituent, but on the other hand is 

 not simply a formless substance filling the spaces between the 

 feldspar. It is uniformly, though with varying degrees of 

 distinctness, grouped in radiating forms, fan-shaped or feather- 

 like, of great variety and beauty. 



This structure is eminently characteristic of this group of 

 rocks. It is shown best in a fine-grained purplish colored speci- 

 men (No. 97, G.=2"82). This is seen under the hand glass to be 

 minutely porous though not properly vesicular, with minute 

 slender red crystals (augite) projecting into the cavities. An 

 occasional grain of chrysolite can be detected in the mass and 

 cleavage sections of feldspar are also seen. Under the microscope 

 it is made ivp of lath-shaped feldspar individuals and the beautiful 

 groupings of augites, these set out in relief by the fine grains 



Feather-forms of augite; a ( x 35), b ( x 35), c ( x 50) from Mokuaweoweo, d ( x 70) 



from Kilauea. 



of iron ore surrounding them. In the simplest cases the augite 

 is bunched together in long parallel groups slightly diverging 

 at the extremities ; generally these branch off at various points 

 into feather-like or dendritic forms, of such variety as to be 



