20 



University of California Publications. 



[Geology 



There is no chlorite or caleite, but in slide 95 there is some epi- 

 dote. The epidote has irregular outline, but its absorption tint 

 (pistachio green), high relief and strong double refraction in 

 nearly equally dimensional sections make its identification quite 

 certain. It has apparently replaced hornblende. A consider- 

 able portion of the feldspar is somewhat elongated in the zone 

 od P cc : OP (100:001). No section normal to co p oo (010), was 

 found in which to measure extinction angles of the albite twins. 

 Carlsbad twins are numerous. In sections nearly parallel to the 

 braehypinaeoid the axial figure is only a little to one side, and 

 the axial plane makes an angle of a few degrees with the most 

 pronounced cleavage, which is the basal. Hence it is quite cer- 

 tain these feldspars are not very basic. Quartz often contains 

 plagioelase, as also does microcline. Apatite and sphene are 

 present, and the latter is frequently of irregular outline and of 

 good size. There is magnetite present, and in slide 95 a black 

 opaque mineral with narrow border of sphene may occasionally 

 be seen, especially in the larger crystals of hornblende. It may 

 be ilmenite. In slide 94 the association of sphene, hornblende, 

 biotite and magnetite is marked. Strain effects are apparent, as 

 many minerals have a wavy extinction and show slight faulting. 

 Apatite needles are broken and slightly displaced. No indication 

 could be obtained that any movement had taken place during 

 the crystallization of the rock. The following analysis was made 



of specimen 94 : 



Per Cent. 



Si0 2 67.70 



*ALO ; , 15.95 



*Fe 2 3 1.53 



*FeO 1.14 



*MgO 1.23 



*CaO 2.70 



*K 2 3.74 



*Na 2 4.83 



H.,0 @ 105° C 0.19 



HoO @ ignition 0.36 



TiO„ 0.23 



MnO, present, not determined. 

 PaOs, present, not determined. 



Total 99.60 



These were duplicated, and were concordant within .06 per cent. 



