670 THE JOURNAL OF GEOLOGY. 



green aggregate, and in the color of the feldspar. This color is 

 a decided pink or red, but there can be no doubt that it is itself 

 a result of alteration, having replaced an original gray like that 

 of the feldspar of the specimens from greater depth. These 

 patches of comparatively little altered granite are only a few 

 feet in diameter, and shade off into the typical serpentine-like 

 rock on all sides. The passage is gradual as a whole, but more 

 rapid in some spots than in others, so that, while it is impossible 

 to draw any line of demarcation in the stages of the process, 

 lines uniting equally altered portions around a granite core would 

 be extremely irregular. 



From the centre of such a core outward the green aggregate 

 increases, while the feldspar gradually disappears, till finally 

 there remains a waxy, deep green mass holding fragments of 

 quartz. In some highly altered specimens the quartz is very 

 conspicuous against the dark groundmass ; in others it is 

 entirely absent, though this is never true of large masses. In 

 still other cases lumps of quartz several inches in diameter 

 occur. These always lie close to one another and usually along 

 definite zones, showing clearly that they are fragments of crushed 

 veins. 



In the slightly altered granite cores there are no conspicuous 

 indications of disturbances, the slickensides being confined to 

 the highly altered phases of the rock, in which, as stated above, 

 they are very prominent. This fact, together with the great 

 irregularity in the direction of the slickensides, suggests that the 

 movements which have formed the polished surfaces may have 

 resulted from changes of bulk in the rock attendant upon the 

 alteration, as in the case of true serpentines. 1 



It should be noted, however, that the granite cores are so 

 small that they might fail to give evidence of considerable 

 movements in the mass as a whole, and such movements may 

 account for the slickensides, as they do for the crushing of the 

 quartz in veins and scattered through the rock. That the latter 



1 J. S. Diller, Geology of the Lassen Peak District, 8th Ann. Rept., U. S. G. S., 

 p. 401. 



