E. S. Dana — Petrography of the Sandwich Islands. 451 



mediate zone the microlites were more numerous and were 

 surrounded by a brown oval aureole of somewhat deeper color 

 than the rest of the glass, this having a beautiful spherulitic 

 structure in polarized light. The nucleus was sometimes 



5. Feldspar microlite surrounded by dark filaments within an oval of brown glass 

 (x90). 



6> Crystallites of various forms ( x 160). All from basaltic glass, Mokuaweoweo. 



transparent (feldspar) and about this were curious dark brown 

 processes thrown off in curved lines (see fig. 5). The highly 

 devitrified portion consisted of a nearly continuous mass of 

 dark brown spherulites and crowded among them numbers of 

 whitish nearly opaque crystallites. Many of the spherulites 

 have a distinct nucleus of chrysolite or feldspar, and sometimes 

 there is a medusa-like mass of dark brown bands radiating out 

 from the nucleus. 



The crystallites (see fig. 6) have sometimes a simple oval 

 form with a faintly indicated structure transverse to the longi- 

 tudinal axis ; there are also compound forms with axes crossing 

 at 90°, making a four-rayed star (b), or at 60° and these last 

 when repeated making a regular six-rayed star (c). Rarely 

 these forms are resolved into a delicate skeleton form of the 

 types indicated (d, e,f) and of many other less regular shapes. 

 Similar forms of " crystalloids " are figured by Vogelsang in 

 plate YII of his work, " Die Krystalliten." 



Chrysolite is distributed through the section in isolated crys- 

 tals or in clusters. These crystals often enclose a considerable 

 amount of the brown glass, and while sharp in outline have 

 sometimes peculiar forms (fig. 4, g) which are interesting in con- 

 nection with the corroded forms met with in the highly crys- 

 talline basalts which have already been described. Feldspar is 

 present in the more highly devitrified portion ; augite not 



