396 GEOLOGY OF THE EUKEKA DISTRICT. 



10. ZIRCON FROM RIIYOL1TK. 



Thin section 205, magnified 100 diameters. Cross section of a zircon crystal, showing only one set 

 of prism faces and a cleavage parallel to the other. 



11. OLIVINK FKOM BASALT OK BASALT PEAK. 



Thin section 282, magnified 78 diameters. Section of oil vine, showing spheroidal fractures and the 

 irregular outline caused hy the crystal losing itself in a multitude of inclusions of augitc and 

 feldspar. The red decomposition is seen taking placo from the cracks, giving the effect of a 

 libration that is parallel throughout the whole crystal. 



12, 13. OLIVINK FROM ISASALT OF BASALT PEAK. 



Thin section 282, magnified 75 diameters. Sections of olivine, showing the same cieavage and decom- 

 position as Fig. 11, in one the alteration setting in from the outside, in the other beginning at 

 the center. 



14. FELDSPAR KKOM KHYOLITE. 



Thin section 145, magnified 550 diameters. Form of feldspar microlitcs, probably oligochisc, round 

 crowded together in a glassy rhyolite. They show various stages, from rectangular compart 

 crystals with sprouting cornel's to the finest libers. 



15. ZIKCON FROM ANDKSITIC PKARLITK. 



Thin section 54, magnified 175 diameters. Long, slender zircon crystal, O'S? 1 "" 1 long, terminated at 

 both ends, lying in groundmoss ; appears to have the form ooP, ooP, 3P3, with P and Poo . 



16. ZIRCON FROM ANDKsVriC PEARLITE. 



Thin section 61, magnified 455 diameters. Long, slender crystal, 0-13 '"" long, lying isolated near tin- 

 edge of the rock section, terminated at one end and broken at the other, with the faces ocp, 

 ooPac, and 3 P 3. 



17. ZIRCON IN ANDESITIC PKARLITK. 



Thin section 75 b, magnified 470 diameters. Stont crystal, 0-09 """ long, lying in glassy groundmass, 

 with apparently ooP, ooPoo , 3 P3, and P or Pao . 



18. ZIRCON FROM RHYOLITE. 



Thin section 168, magnified 540 diameters. Simple crystal of zircon, 0'08 nlm long, inclosed in 

 feldspar, formed of a single prism and the alternate pyramid. 



19. ZIRCON FROM ANDKSITIC PKARLITE. 



Thin section 58, magnified 900 diameters. Crystal of zircon, 0-044""" long, occurring in feldspar 

 and appearing to have the faces ooP, ooPoo, 3P3, P, and Poo. 



20. ZIRCON FROM AXDESITIC PEARLITE. 



Thin section 73, magnified 570 diameters. Crystal of zircon, 0-06 mn > long, in feldspar, having ooP, 

 ooPoo, 3P3, and two pyramids. 



