Lawson.] 



The Upper Kern Basin. 



The microscope shows phenocrysts of hornblende and feldspar 

 in a panidiomorphic ground. This structure is caused by the 

 recurrence of the hornblende and feldspar in two generations. 

 Accessory magnetite and apatite are present. The hornblende is 

 brown; that of the first period is developed in broad prisms, the 

 transverse partings of which often contain biotite. That of the 

 second has crystallized in slender needles, often showing a fluidal 

 arrangement around the feldspar phenocrysts. The feldspar of 

 the first generation occurs as large Carlsbad twins, turbid and 

 heavily sprinkled with grains of opaque material. The idiomor- 

 phic development of the feldspar of the second generation equals 

 that of the hornblende of the same period. Orthoclase is the 

 dominant feldspar, plagioclase occurring in subordinate amount. 

 The hornblende comprises about 40 per cent, of the bulk of 

 the rock. 



The other specimen of vogesite differs in only minor respects 

 from the last. The phenocrysts of green hornblende and feld- 

 spar are contained in a ground consisting of laths of hornblende 

 and biotite, and shapeless patches of hornblende and feldspar. 

 In parallel light the feldspar appears to be homogeneous, but 

 between crossed uicols resolves into a mosaic of small grains 

 showing an undulous extinction. The hornblende of the first 

 generation occurs occasionally in large prisms intergrown with 

 some biotite. Nearly 40 per cent, of the rock is hornblende. The 

 feldspar of the phenocrysts exhibits marked zonary banding; 

 trains of inclusions parallel to the two cleavages give it a dusty 

 appearance. Remains of other large crystals are indicated by 

 the aggregation of decomposition products. Albite lamellation 

 is very rare, othoclase being the dominant feldspar. 



One of the camptonite dykes from the west side of Upper 

 Kern Lake is a fine grained, gray rock, showing prisms of horn- 

 blende and occasional feldspars. Structurally the rock is a 

 panidiomorphic aggregate of green hornblende and feldspar, with 

 accessory apatite and magnetite. The idiomorphism of the horn- 

 blende is poor, the crystal edges being ragged and irregular. 

 Twinning is common. Some tendency toward a fluidal arrange- 

 ment is indicated both by the development of long, slender prisms 

 and the parallelism of their major axes. The hornblende 



