82 THE CRYSTAL FALLS lEON-BEARl^STG DISTRICT. 



of the black cross of imiaxial minerals into hyperbolae. Embayments of 

 grouudniass, and liquid inclusions in which a dancing bubble may be seen, 

 are in places rather thickly distributed through the quartz. The liquid 

 inclusions have very commonly an hexagonal fonn, corresponding to the 

 contours of the inclosing quartz. 



These liquid inclusions are certainly in some cases secondary. This 

 character is well shown in some of the crystals, which ai-e broken across, 

 giving along the line of fracture a very wavy extinction. Along this line 

 of fracture the greatest quantity of inclusions are seen, both with and 

 without bubbles. As the distance fi-om a fracture increases, both the undu- 

 latory extinction and the number of inclusions diminish. (See fig. A, 

 PI. XIX.) These fractures in the quartzes are but continuations of those 

 which extend in many cases all the way across the section. The fractm-es 

 have since been healed by secondary quartz. This secondary quartz has 

 also in some cases healed the fractured quartz phenocrysts, and then agrees 

 with them in orientation. The possession of an imperfect rhombohedral 

 parting is very noticeable in a number of quartzes, and especially those 

 wlaich, being on the edge of the section, are very tliin. (See fig. B, PI. 

 XIX.) Similar parting in the quartz occurs in various rocks studied in this 

 district. 



The phenocrysts of the porphp-ies are traversed by fractures, some of 

 which are more or less circular, and simulate very imperfectly perlitic cracks. 

 With the exception of those in porphyries in two localities, the quartz 

 phenocrysts are surrounded by zones, largely of quartz, of varjring widths, 

 and considerably lighter than the remainder of the groundmass. Much of 

 the quartz of these zones has the same optical orientation as the phenocrysts. 

 In those sections in which the zones are observed they occur around every 

 section of quartz. 



The feldspar phenocrysts are orthoclase and plagioclase, the latter 

 apparently predominating. They occur usually in rounded, badly corroded 

 crystals, with indentations filled with groundmass. They are always altered, 

 and have associated with them as secondary products calcite, epidote, 

 muscovite, biotite, and chlorite 



No large original ferro-magnesian phenocrysts appear to have been 

 present in the porphp-y. Their former presence is at least not indicated 

 by any aggregates of secondary products. Whatever ferro-magnesian min- 



