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University of California Publications in Geology [ VoL 11 



Muscovite is a common constituent and fresh green or brown biotite 

 often occurs. Augite and hornblende are occasionally seen. 



Magnetite occurs in small amounts. Usually it is disseminated 

 throughout the rock. Occasionally it becomes more important and is 

 segregated in bands which may reach a thickness of a quarter of an 

 inch. In such instances it occurs in association with zircon and other 

 heavy minerals. Mr. F. E. Turton 41 found monazite in one of these 

 magnetite bands. Pyrite occasionally occurs in single crystals in the 

 sandstone. 



Zircon is au important minor constituent. It occurs in large grains 

 of a size comparable with the other clastic grains of the sandstone. 

 Also it is found as small columnar crystals with acute pyramidal ter- 

 minations, included in the grains of quartz and feldspar. 



Epidote is a rather common constituent of the sandstone. It 

 occurs in clastic grains of moderately large size. It is also found 

 occasionally in minute crystals in the cement. Here it may be a sec- 

 ondary mineral. 



Large grains and flakes of chlorite which seem to be original con- 

 stituents of the sand are frequently present. Minute scales, probably 

 often secondary, are found in the cement. In some sections, also, a 

 pale greenish tinge may be observed in the cementing material, which 

 probably represents finely disseminated chlorite. Grains of serpentine 

 are found frequently. In size these are comparable with the other 

 clastic grains. An occasional fragment may be much larger. 



A very few grains of pale flesh-colored garnet have been noted in 

 the thin sections. 



Besides the grains of single minerals, small fragments of rocks are 

 often present. Angular blocks and splinters of granitic rock, consist- 

 ing of quartz and plagioclase feldspar are occasionally found. Dia- 

 base fragments are common. Angular fragments of vein quartz and 

 of chalcedonic silica are common. One fragment of quartz-biotite 

 schist was noted, and angular fragments of black shale are very 

 numerous. 



In a few cases where the interstitial spaces are large, the clastic 

 grains are embedded in a matrix of minute mineral fragments — 

 chiefly quartz and feldspar. In a few instances there seems to have 

 been little change in the grains of finer material, but in others the 

 cement appears to be largely recrystallized. 



The larger grains of the sandstone have undergone little recrystal- 



41 Unpublished notes. 



