Plate 30 



^Photomicrograph of no. 163-a. Taken with plain hght, magnification about 25 diameters. 

 Taken particularly to show the intimate penetration of injection matters, especially quartz. 

 ,_JThe grayish portion of the field is chiefly made up of slightly altered feldspar and associated 

 ■quartz. These are cut by later quartz which appears in clear bands which, if followed farther in 

 the slide, can be seen to widen or narrow and sometimes pinch out entirely as they extend into the 

 ■wider material. 



Plate 31 



Photomicrograph of no. 163-6. Taken with plain light, magnification about 25 diameters. A 

 second photomicrograph taken from the same slide as no. 163-a. 



The field shows a similar habit to 163-0 in that the older rock material is represented by the 

 grayish bands and the newly introduced quartz by the clear colorless bands. 



The older rock material is represented by slightly altered orthoclase and microline, by a little 

 quartz in small grains, and by pseudomorphs made up of secondary chloritic aggregates. 



Some of these, no doubt, represent former ferro-magnesian minerals and are very dark. The 

 subsequently injected matter is quartz which cuts through and into the older material in tongue-like 

 stringers and narrow bands. Three of these are distinctly represented in this fi.eld, the central and 

 widest one terminating within the bounds of this particular field. One of the others is a very narrow 

 and somewhat broken looking stringer and at the opposite side of the field a third band wedges 

 out to almost nothing. 



