Lawson.] 



The Upper Kern Basin. 



375 



spar showing nndulons extinction occur. A few small laths of 

 plagioclase have formed, giving' extinction angles of 30° and 

 corresponding to acid Iabradorite. 



Angite has crystallized out in two generations, the first, how- 

 ever, occurring sporadically as inconspicuous phenocrysts which 

 have often been stained red from oxides of iron. 



The Lavas of Volcano Creel-. — These lavas differ from the 

 older lavas of the Little Kern Plateau in containing abundant 

 olivine. Three specimens were examined microscopically, all 

 being olivine basalts. The first of these is characterized as 

 follows : 



Macroscopically it is somewhat vesicular and of blue gray 

 color. It possesses a conspicuous porphyritic structure, contain- 

 ing numerous plagioclase laths and olivine phenocrysts embedded 

 in a fine grained matrix. Under the microscope the phenocrysts 

 are seen to consist of plagioclase, olivine and angite. The 

 gronndniass is a dense aggregate of plagioclase microlites and 

 small allotriomorphic patches of feldspar, containing abundant 

 granules of angite and magnetite. The plagioclase microlites 

 give an extinction angle of 31°, indicating them to be Iabradorite. 

 The plagioclase of the first generation occurs in long laths 

 showing albite lamellation, A few are untwinned and these 

 commonly exhibit a marked zonary banding. They often grade 

 in the direction of elongation into the feldspar of the ground 

 mass. Olivine is a very abundant constituent, but has suffered 

 marked chemical corrosion. The angite of the phenocrysts 

 occurs in smaller amount than the olivine, and is developed in 

 short stout prisms, usually surrounded by heavy borders of iron 

 oxides. 



The second rock from Volcano Creek in the hand specimen is 

 an exceedingly compact, line grained dark rock. Only an occa- 

 sional small phenocryst of plagioclase is visible. The microscope 

 shows a pilotaxitic structure with a marked fluidal arrangement 

 of the microlites. The phenocrysts are neither large nor numer- 

 ous, and consist of plagioclase, olivine and angite. Angite and 

 magnetite granules are abundant. The microlites yield an 

 extinction angle of 32°. thus fixing them as Iabradorite. The 

 plagioclase phenocrysts exhibit marked chemical corrosion, in 



