50 CALIFORNIA ACADEMY OF SCIENCES. 



KagO : ii.T,6i, NagO : 2.14/^. 77//;/ secfio)i: The pheno- 

 crysts mentioned above are imbedded in a holocrystalline 

 groundmass, composed of sanidine crystals of varying 

 size, augite prisms and small foils of biotite. No plagio- 

 clase noted: there is in fact, a gradual transition from the 

 phenocrysts down to the smallest individuals. Possibly 

 some glass between the crystals of the groundmass. x\p- 

 atite in clear, short prisms. 



In a series of dike rocks, closely allied to the one just 

 described, the augite gradually increases in quantity. In 

 a specimen from the southern slope, for instance, the san- 

 idines are much smaller and thinner: there is at least as 

 much augite as sanidine: the groundmass still contains 

 sanidine predominantly, usually in form of short prisms 

 with extinctions ranging from o^ up to 5' \ Besides there 

 are a few plagioclase-microlites. 



r. Finally the porphyritic sanidine disappears and the 

 augite in dark green, long prisms takes its place ; the 

 groundmass is dark gray or dark green ; these rocks form 

 the third type. No. 35 shows in thin-section large por- 

 phyritic augites of prismatic habit and light green color, 

 together with some partly idiomorphic olivine crystals im- 

 bedded in a clear groundmass consisting of grains and 

 microlites of feldspar, cemented by colorless glass. The 

 feldspars when showing cr^^stalline form have a short 

 prismatic habit and are not striated, but sometimes form 

 Carlsbad twans ; the glass is colorless and easily dissolves 

 in HCl. In this class of rocks the feldspars should be 

 more investigated, by chemical analysis and by separa- 

 tions. 



IV. Plagioclase Basaet. 



There are a few rocks among the dikes of the High- 

 wood Mountains which might be classed as plagioclase 



