Lawson "I 

 PalacheJ 



The Berkeley Hills. 



413 



distinct, but more usually zoning is merely evidenced by undula- 

 tory extinction. In all observed cases the inner portion of the 

 zoned crystals extinguished at a higher angle to the axis of elonga- 

 tion than the peripheral portions. Many crystals which appear 

 quite clear reveal under high powers the presence of clouds of 

 minute dusty bodies which are scattered irregularly through the 

 mass of the crystal, and are wholly undeterminable. In addition 

 to these, which seem to be always present, are found inclusions of 

 glass, augite and its alteration product, serpentine, magnetite, and 

 apatite. The distribution of these inclusions is exceedingly irregu- 

 lar, but as a rule the largest phenocrysts show them more charac- 

 teristically. The glass occurs in irregular branching areas, or in 

 rounded blebs sometimes containing a black-bordered gas bubble. 

 It is brown to black in color and generally crowded with dusty 

 black specks, probably of magnetite. It is most common in the 

 phenocrysts of glassy facies of the rock, but also occurs in holo- 

 crystalline forms. Augite forms rounded grains or branching 

 patches sometimes so numerous as to nearly equal in bulk the mass 

 of the feldspar host. No order is perceptible in their arrangement 

 with reference to one another, but they are sometimes grouped 

 more or less regularly with reference to the boundaries of the host. 

 This grouping is either in a sharply-defined central zone, in a 

 narrow peripheral zone, or in an intermediate zone with clear 

 spaces within and without. In one or two instances only were the 

 augite inclusions seen to have a uniform orientation over consider- 

 able spaces, giving rise to an appearance of micropegmatitic inter- 

 growth. The decomposition of these augite inclusions to serpen- 

 tine is common, and the increased bulk of the mineral causes it to 

 migrate into the cracks and cleavages of the host. The appearance 

 of these augite inclusions is perfectly represented in the figure in 

 Rosenbusch Mile. Phys., Plate XXIV, fig. 3, although in that plate 

 the inclusions are of glass. Magnetite and apatite occur in char- 

 acteristic forms in greater or less abundance without definite group- 

 ing. Movements of the unconsolidated magma are evidenced by 

 numerous cracked and broken crystals, their fractured surfaces 

 separated by bands of intruded ground-mass. Corroded pheno- 

 crysts are also seen, and occasionally the shadowy outline of 



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