396 GEOLOGY OF THE EUKEKA DISTKIGT, 



10. ZIKCDX Fi;o,M RIIYOLITK. 



Thin section 205, magnified 100 iliameters. Cross seiticm uf a zircon crystal, showing only one set 

 of prism faces ami a cleavage parallel to the other. 



11. OI.IVINK FROM BASALT OF BA.SAI.l' 1M:ak. 



Thin section 282, magnified 78 diameters. Section of olivine, showing spheroidal fraoturci 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 place from the cracks, giving the effect of a 

 liliratiou that is parallel througlioiit the whole cryst:il. 



12, 13. OI.IVINK FROM BASALT OP BASALT PEAK. 

 Thin sectioH 282, magnified 7."> dianu'ters. Sections of olivine, showing the same cieavage and decom- 

 position as Fig. 11, in one the alteration setting in li'om the outside, in the other beginninn' at 

 the center. 



14. FELDSPAR FROM KHYOLITE. 

 Thin section 145, magnified 550 diameters. Form of feldspar microlites, probably oligoclasc, ioniul 

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

 crystals with sprouting corners to the finest fibers. 



15. ZIKCON FROM A.VDE.smc PEARLITK. 



Thin section 54, magnified 175 diameters. Long, sleu<ler zircon crystal, O-S?"'™ long, terminated at 

 both ends, lying in groundmass; appears to have the form ooP, <xP», 3P3, with P and Px . 



16. ZIRCON FROM AXDKSITIC PEARLITE. 



Thin section 61, magnified 455 diaiuetcis. Long, slender crystal, 0-13 ■"'" long, lying isolated near tln^ 

 edge of the rock sectiou, terminated at one end and broken at the other, with the faces ocP 

 ooPoo, and 3 P 3. 



17. ZIRCON IN ASDESITIC PEARLITE. 



Thin section lob, magnified 470 diameters. Stout crystal, O-O!}""" long, lying in glassy groundmass 

 with apparently ocP, acPoo. 3P3, and P or Px . 



18. ZIRCON FRO.'H RItYoLITE. 



Thin section 168, magnified 540 diameters. Simple crystal of zircon, 0-08""" long, im-losi'd in 

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



19. ZIRCON FROM ANDESITIC PEARLITE. 



Thin section 58, magnified 900 diameters. Crystal of zircon, 0044 ' hnig, occurring in feldspar 



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



20. ZIRCON FROM .\KDESITIC PEARLITE. 



Thin section 73, magnified 570 diamctiiis. Crystal of zircon, 006""" long, in feldspar, having ooP 

 ooPoo, 3P3, and two pyramids. 



